Wireless power transfer systems with shield openings

ABSTRACT

In a first aspect, the disclosure features apparatuses for wireless power transfer, the apparatuses including a plurality of magnetic elements joined together to form a magnetic component extending in a plane, where discontinuities in the magnetic component between adjacent magnetic elements define gaps in the magnetic component, a coil including one or more loops of conductive material positioned, at least in part, on a first side of the plane. The apparatuses include a conductive shield positioned on a second side of the plane and which includes one or more openings positioned relative to the gaps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. § 120 to U.S. application Ser. No. 14/688,025, filed on Apr. 16,2015, which claims priority to U.S. Provisional Patent Application No.61/980,712, filed on Apr. 17, 2014. The entire contents of theabove-referenced applications incorporated herein by reference in theirentirety.

TECHNICAL FIELD

This disclosure relates to wireless power transfer.

BACKGROUND

Energy can be transferred from a power source to a receiving deviceusing a variety of known techniques such as radiative (far-field)techniques. For example, radiative techniques using low-directionalityantennas can transfer a small portion of the supplied radiated power,namely, that portion in the direction of, and overlapping with, thereceiving device used for pick up. In this example, most of the energyis radiated away in directions other than the direction of the receivingdevice, and typically the transferred energy is insufficient to power orcharge the receiving device. In another example of radiative techniques,directional antennas are used to confine and preferentially direct theradiated energy towards the receiving device. In this case, anuninterruptible line-of-sight and potentially complicated tracking andsteering mechanisms are used.

Another approach is to use non-radiative (near-field) techniques. Forexample, techniques known as traditional induction schemes do not(intentionally) radiate power, but use an oscillating current passingthrough a primary coil, to generate an oscillating magnetic near-fieldthat induces currents in a near-by receiving or secondary coil.Traditional induction schemes can transfer modest to large amounts ofpower over very short distances. In these schemes, the offset tolerancesbetween the power source and the receiving device are very small.Electric transformers and proximity chargers use these traditionalinduction schemes.

SUMMARY

This disclosure relates to wireless transfer systems utilizing wirelesspower transfer of power from a power transmitting apparatus to a powerreceiving apparatus. To achieve high power transfer efficiency, thepower transmitting apparatus and/or the power receiving apparatus caninclude a magnetic component and a shield to facilitate the powertransfer. Particularly, it can be advantageous to have a large magneticcomponent in transferring high power for some applications. However,manufacturing the large magnetic component as a single monolithic piececan be impractical or expensive because materials such as ferrites canbe difficult to fabricate and/or easily break. Thus, the large magneticcomponent can instead be formed by combining smaller magnetic elementstogether. In this approach, the magnetic elements are typically joinedacross one or more gaps, which can be filled with air or adhesive forconnecting the magnetic elements. Such gaps can be problematic, however,because magnetic fields can be concentrated at regions of the gaps. Theconcentrated magnetic fields can penetrate the nearby shield and othermaterials or structures and induce eddy currents, thereby leading tolosses in the systems and reductions in the amount of power transferred.To address such issues, this disclosure describes a variety ofconfigurations of magnetic components and shields to mitigate lossesinduced by penetration of magnetic fields into the shields, for example,by aligning openings of the shields to gaps of the magnetic components.

In a first aspect, the disclosure features apparatuses for wirelesspower transfer, the apparatuses including a plurality of magneticelements joined together to form a magnetic component extending in aplane, where discontinuities in the magnetic component between adjacentmagnetic elements define gaps in the magnetic component, and a coilincluding one or more loops of conductive material positioned, at leastin part, on a first side of the plane. The apparatuses include aconductive shield positioned on a second side of the plane and which theshield includes one or more openings positioned relative to the gaps.

Embodiments of the apparatuses can include any one or more of thefollowing features.

The openings can be respectively aligned with corresponding ones of thegaps. The one or more openings can be positioned relative to the gaps toreduce interactions between magnetic flux crossing the discontinuitiesand the conductive shield.

The coil can be positioned entirely on the first side of the plane. Theone or more loops of conductive material can wrap around the magneticcomponent. The conductive shield can be substantially parallel to theplane. The one or more openings can extend entirely through the shield.

The plane can extend in orthogonal first and second directions, andwhere the one or more loops of conducting material wrap around a thirddirection perpendicular to the first and second directions (i.e.,perpendicular to the plane). The gaps can include a first gap having alongest dimension extending in the first direction, and the one or moreopenings can include a first opening having a longest dimensionextending in a direction substantially parallel to the first direction.The first gap can have a maximum width measured in a direction parallelto the second direction, the first opening can have a maximum widthmeasured in a direction parallel to the second direction, and themaximum width of the first opening can be larger than the maximum widthof the first gap. A ratio of the maximum width of the first opening to acharacteristic size of the magnetic component can be 1:10 or less.

During operation, the coil can generate a magnetic field that oscillatesin a direction parallel to the second direction. A first one of the gapscan correspond to a spacing between magnetic elements in a directionparallel to the second direction, and a first one of the one or moreopenings can be aligned with the first one of the gaps and include awidth that extends in a direction parallel to the second direction. Eachof the gaps can correspond to a spacing between magnetic elements in adirection parallel to the second direction, and each of the one or moreopenings can be aligned with a corresponding one of the one or more gapsand includes a width that extends in a direction parallel to the seconddirection.

The coil can be electrically isolated from the conductive shield.

The one or more loops can include a first plurality of loops concentricabout a first axis and a second plurality of loops concentric about asecond axis, where the first and second axes are parallel to the thirddirection. The first plurality of loops can be wound in a firstconcentric direction about the first axis, and the second plurality ofloops can be wound about the second axis in a second concentricdirection opposite to the first concentric direction, when measured froman end of the first plurality of loops towards an end of the secondplurality of loops. During operation, the coil can generate a magneticfield within the magnetic component that oscillates in a directionparallel to the second direction.

The plurality of magnetic elements can form an array. The plurality ofmagnetic elements can include 4 or more magnetic elements. At least oneof the gaps can include air spaces. At least one of the gaps can includea dielectric material positioned between the magnetic elements. Forexample, the dielectric material can include an adhesive material.

At least some of the plurality of magnetic elements can be formed of aferrite material. The ferrite material can include at least one materialselected from the group consisting of MnZn-based materials, NiZn-basedmaterials, amorphous cobalt-based alloys, and nanocrystalline alloys.

The coil can be configured to wirelessly transfer power to, or receivepower from, another coil. A minimum distance between a surface of themagnetic component and the shield can be 1 mm or less.

At least one of the openings can include lateral surfaces that areangled with respect to the plane.

At least one of the openings can include a triangular cross-sectionalprofile. At least one of the openings can include a trapezoidalcross-sectional profile. At least one of the openings can include across-sectional profile having one or more curved edges.

At least one of the gaps can be with a magnetic material comprising amagnetic permeability different from a magnetic permeability of theplurality of magnetic elements.

In another aspect, the disclosure features apparatuses for wirelesspower transfer, the apparatuses including a plurality of magneticelements joined together to form a magnetic component extending in aplane, where discontinuities in the magnetic component between adjacentmagnetic elements define gaps in the magnetic component. The apparatusesinclude a coil comprising one or more loops of conductive materialpositioned, at least in part, on a first side of the plane, and aconductive shield positioned on a second side of the plane and where theshield includes one or more depressions formed in a surface of theshield facing the magnetic component. Each of the one or moredepressions is positioned relative to the gaps.

Embodiments of the apparatuses can include any one or more of thefollowing features.

The one or more depressions can be respectively aligned withcorresponding ones of the gaps. The one or more depressions can bepositioned relative to the gaps to reduce interactions between magneticflux crossing the discontinuities and the conductive shield. At leastone of the depressions can form an opening that extends entirely througha thickness of the shield.

The coil can be positioned entirely on the first side of the plane. Theplane can extend in orthogonal first and second directions, where theone or more loops of conducting material can wrap around a thirddirection perpendicular to the first and second directions (i.e.,perpendicular to the plane). The one or more loops of conductivematerial wrap around the magnetic component. The conductive shield canbe substantially parallel to the plane.

The one or more depressions can include lateral surfaces that are angledwith respect to a surface of the shield facing the magnetic component. Awidth of the one or more depressions measured at the surface of theshield facing the magnetic component can be larger than a width of theone or more depressions measured at another location between the lateralsurfaces.

At least one of the depressions can include a cross-sectional profilehaving a triangular shape. At least one of the depressions can include across-sectional profile having a trapezoidal shape. At least one of thedepressions can include a cross-sectional profile having one or morecurved edges. At least one of the depressions can correspond to a curvedgroove formed in the shield.

The one or more loops can include a first plurality of loops concentricabout a first axis and a second plurality of loops concentric about asecond axis parallel to the first axis, and the first and second axescan be orthogonal to the plane of the magnetic component. The firstplurality of loops can be wound in a first concentric direction aboutthe first axis, and the second plurality of loops can be wound about thesecond axis in a second concentric direction opposite to the firstconcentric direction, when measured from an end of the first pluralityof loops towards an end of the second plurality of loops.

During operation, the coil can generate a magnetic field within themagnetic component that oscillates in a direction parallel to a width ofat least one of the depressions.

The gaps can include a first gap having a longest dimension extending ina first direction, and the depressions can include a first depressionhaving a longest dimension extending in a direction substantiallyparallel to the first direction. The first gap can have a maximum widthmeasured in a direction perpendicular to the longest dimension of thefirst gap. The first depression can have a maximum width measured in adirection perpendicular to the longest dimension of the firstdepression, and the maximum width of the first opening can be largerthan the maximum width of the first gap.

Each of the gaps can correspond to a spacing between magnetic elementsin a direction perpendicular to the first direction, and each of thedepressions can be aligned with a corresponding one of the gaps and canhave a width that extends in a direction perpendicular to the firstdirection.

The plurality of magnetic elements can form an array. The plurality ofmagnetic elements can include 4 or more magnetic elements.

At least one of the one or more gaps can include air spaces. At leastone of the one or more gaps can include a dielectric material positionedbetween the magnetic elements. For example, the dielectric material caninclude an adhesive material.

At least some of the plurality of magnetic elements can be formed of aferrite material. The ferrite material can include at least one materialselected from the group consisting of MnZn-based materials, NiZn-basedmaterials, amorphous cobalt-based alloys, and nanocrystalline alloys.

The coil can be configured to wirelessly transfer power to, or receivepower from, another coil.

A ratio of the maximum width of the first depression to a characteristicsize of the magnetic component can be 1:10 or less. A minimum distancebetween a surface of the magnetic component and the shield can be 1 mmor less. At least one of the gaps is filled with magnetic material canhave a magnetic permeability different from a magnetic permeability ofthe magnetic elements.

In another aspect, the disclosure features methods for wirelesslytransferring power using apparatuses, the methods including wirelesslytransferring power from a power transmitting apparatus to a powerreceiving apparatus, where at least one of the power transmittingapparatus and the power receiving apparatus includes: a magneticcomponent extending in a plane and formed from a plurality of magneticelements joined together, where discontinuities in the magneticcomponent between adjacent magnetic elements define gaps in the magneticcomponent, a coil including one or more loops of conductive materialpositioned, at least in part, on a first side of the plane, and aconductive shield positioned on a second side of the plane andcomprising one or more openings positioned relative to the gaps.

The power transmitting apparatus and the power receiving apparatus caneach include the magnetic component, the coil, and the conductiveshield.

Embodiments of the apparatuses and methods can also include any otherfeatures disclosed herein, including features disclosed in connectionwith other apparatuses and methods, in any combination as appropriate.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. In case of conflict withpublications, patent applications, patents, and other referencesmentioned or incorporated herein by reference, the present disclosure,including definitions, will control. Any of the features described abovemay be used, alone or in combination, without departing from the scopeof this disclosure. Other features, objects, and advantages of thesystems and methods disclosed herein will be apparent from the followingdetailed description and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless power transfer system.

FIG. 2 is a schematic diagram of an example of a power transmittingapparatus.

FIG. 3 is a schematic diagram showing a cross-sectional view of thepower transmitting apparatus shown in FIG. 2.

FIGS. 4A and 4B are schematic diagrams showing an example of a powertransmitting apparatus.

FIG. 5 is a schematic diagram of a portion of the power transmittingapparatus shown in FIGS. 4A and 4B.

FIG. 6 is a schematic diagram of a cross-section of the powertransmitting apparatus shown in FIGS. 4A, 4B and 5.

FIG. 7A-C are schematic diagrams showing examples of power transmittingapparatuses.

FIG. 7D is a schematic diagram of a magnetic component used inapparatuses shown in FIGS. 7B and 7C.

FIG. 8 is a plot showing measured and simulated quality factor values ofthe power transmitting apparatuses shown in FIGS. 7A-C.

FIG. 9 is a plot showing simulated values of Q_(shield) for an apparatusshown in FIG. 7C.

FIGS. 10A and 10B are schematic diagrams showing cross-sectional viewsof two examples of power transmitting apparatuses.

FIG. 10C is a schematic diagram showing the magnetic component describedin FIGS. 10A and 10B and its characteristic size.

FIGS. 11A and 11B are schematic diagrams showing two examples of a powertransmitting apparatuses.

FIG. 12 is a plot showing simulated values of Q_(shield) for apparatusesshown in FIGS. 7C, 11A and 11B.

FIGS. 13A and 13B are schematic diagrams showing two examples of powertransmitting apparatuses.

FIG. 14 is a plot 1400 showing simulated values of Q_(shield) forapparatuses shown in FIGS. 13A and 13B.

FIG. 15A shows three images of an example of a power transmittingapparatus.

FIG. 15B shows two images of an example of another power transmittingapparatus.

FIG. 16 is a plot showing measured values of Q_(trans) of apparatusesshown in FIGS. 15A and 15B.

FIG. 17 is a plot showing measured values of Q_(shield) of apparatusesshown in FIGS. 15A and 15B.

FIG. 18A is a schematic diagram showing an example of a shield.

FIGS. 18B and 18C are schematic diagrams showing an example of a shield.

FIG. 18D is a schematic diagram showing an example of a shield.

FIG. 18E is a schematic diagram showing an example of a shield.

FIG. 18F is a schematic diagram showing an example of a shield.

FIG. 18G is a schematic diagram showing an example of a shield.

FIG. 19A is a schematic diagram of an example of a power transmittingapparatus.

FIG. 19B is a schematic diagram of a cross-section of an example of apower transmitting apparatus.

FIG. 19C is a schematic diagram of a cross-section of an example of apower transmitting apparatus.

FIG. 19D is a schematic diagram of a cross-section of an example of apower transmitting apparatus.

FIG. 19E is a schematic diagram showing an example of a magneticcomponent.

FIGS. 19F-J are schematic diagrams showing examples of several magneticcomponents.

FIG. 20A is a schematic diagram showing an additional example of a coilin a power transmitting apparatus.

FIG. 20B is a schematic diagram showing another example of a coil in apower transmitting apparatus.

FIG. 21 is a schematic diagram showing another example of a coil in apower transmitting apparatus.

FIG. 22 is a schematic diagram showing an example of a powertransmitting apparatus.

FIG. 23 is a schematic diagram showing an example of a powertransmitting apparatus.

FIGS. 24A-C are schematic diagrams showing an example of a powertransmitting apparatus.

FIG. 25 is a block diagram of a computing device.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Introduction

FIG. 1 is a schematic diagram of a wireless power transfer system 100.System 100 includes a power transmitting apparatus 102 and a powerreceiving apparatus 104. Power transmitting apparatus 102 is coupled topower source 106 through a coupling 105. In some embodiments, coupling105 is a direct electrical connection. In certain embodiments, coupling105 is a non-contact inductive coupling. In some embodiments, coupling105 can include an impedance matching network (not shown in FIG. 1).Impedance matching networks and methods for impedance matching aredisclosed, for example, in commonly owned U.S. patent application Ser.No. 13/283,822, published as US Patent Application Publication No.2012/0242225, the entire contents of which are incorporated herein byreference.

In similar fashion, power receiving apparatus 104 is coupled to a device108 through a coupling 107. Coupling 107 can be a direct electricalconnection or a non-contact inductive coupling. In some embodiments,coupling 107 can include an impedance matching network, as describedabove.

In general, device 108 receives power from power receiving apparatus104. Device 108 then uses the power to do useful work. In someembodiments, for example, device 108 is a battery charger that chargesdepleted batteries (e.g., car batteries). In certain embodiments, device108 is a lighting device and uses the power to illuminate one or morelight sources. In some embodiments, device 108 is an electronic devicesuch as a communication device (e.g., a mobile telephone) or a display.In some embodiments, device 108 is a medical device which can beimplanted in a patient.

During operation, power transmitting apparatus 102 is configured towirelessly transmit power to power receiving apparatus 104. In someembodiments, power transmitting apparatus 102 can include a source coil,which can generate oscillating fields (e.g., electric, magnetic fields)when electrical currents oscillate within the source coil. The generatedoscillating fields can couple to power receiving apparatus 104 andprovide power to the power receiving apparatus through the coupling. Toachieve coupling between power transmitting apparatus 102 and powerreceiving apparatus 104, the power receiving apparatus 104 can include areceiver coil. The oscillating fields can induce oscillating currentswithin the receiver coil. In some embodiments, either or both of thesource and receiver coils can be resonant. In certain embodiments,either or both of the source and receiver coils can be non-resonant sothat the power transfer is achieved through non-resonant coupling.

In certain embodiments, the system 100 can include a power repeatingapparatus (not shown in FIG. 1). The power repeating apparatus can beconfigured to wirelessly receive power from the power transmittingapparatus 102 and wirelessly transmit the power to the power receivingapparatus 104. The power repeating apparatus can include similarelements described in relation to the power transmitting apparatus 102and the power receiving apparatus 104 above.

System 100 can include an electronic controller 103 configured tocontrol the power transfer in the system 100, for example, by directingelectrical currents through coils of the system 100. In someembodiments, the electronic controller 103 can tune resonant frequenciesof resonators included in the system 100, through coupling 109. Theelectronic controller 103 can be coupled to one or more elements of thesystem 100 in various configurations. For example, the electroniccontroller 103 can be only coupled to power source 106. The electroniccontroller 103 can be coupled to power source 106 and power transmittingapparatus 102. The electronic controller 103 can be only coupled topower transmitting apparatus 102. In some embodiments, coupling 109 isdirect connection. In certain embodiments, coupling 109 is a wirelesscommunication (e.g., radio-frequency, Bluetooth communication). Thecoupling 109 between the electronic controller 103 can depend onrespective one or more elements of the system 100. For example, theelectronic controller 103 can be directly connected to power source 106while wirelessly communicating with power receiving apparatus 104.

In some embodiments, the electronic controller can configure the powersource 106 to provide power to the power transmitting apparatus 102. Forexample, the electronic controller can increase the power output of thepower source 106 sent to the power transmitting apparatus 102. The poweroutput can be at an operating frequency, which is used to generateoscillating fields by the power transmitting apparatus 102.

In certain embodiments, the electronic controller 103 can tune aresonant frequency of a resonator in the power transmitting apparatus102 and/or a resonant frequency of a resonator in the power receivingapparatus 104. By tuning resonant frequencies of resonators relative tothe operating frequency of the power output of the power source 106, theefficiency of power transfer from the power source 106 to the device 108can be controlled. For example, the electronic controller 103 can tunethe resonant frequencies to be substantially the same (e.g., within0.5%, within 1%, within 2%) to the operating frequency to increase theefficiency of power transfer. The electronic controller 103 can tune theresonant frequencies by adjusting capacitance values of respectiveresonators. To achieve this, for example, the electronic controller 103can adjust a capacitance of a capacitor connected to a coil in aresonator. The adjustment can be based on the electronic controller103's measurement of the resonant frequency or based on wirelesscommunication signal from the apparatuses 102 and 104. In certainembodiments, the electronic controller 103 can tune the operatingfrequency to be substantially the same (e.g., within 0.5%, within 1%,within 2%) to the resonant frequencies of the resonators.

In some embodiments, the electronic controller 103 can control animpedance matching network in the system 100 to optimize or de-tuneimpedance matching conditions in the system 100, and thereby control theefficiency of power transfer. For example, the electronic controller 103can tune capacitance of capacitors or networks of capacitors included inthe impedance matching network connected between power transmittingapparatus 102 and power source 106. The optimum impedance conditions canbe calculated internally by the electronic controller 103 or can bereceived from an external device.

In some embodiments, wireless power transfer system 100 can utilize asource resonator to wirelessly transmit power to a receiver resonator.For example, power transmitting apparatus 102 can include a sourceresonator that includes a source coil, and power receiving apparatus 104can include a receiver resonator that includes a receiver coil. Powercan be wirelessly transferred between the source resonator and thereceiver resonator.

In this disclosure, “wireless energy transfer” from one coil (e.g.,resonator coil) to another coil (e.g., another resonator coil) refers totransferring energy to do useful work (e.g., electrical work, mechanicalwork, etc.) such as powering electronic devices, vehicles, lighting alight bulb or charging batteries. Similarly, “wireless power transfer”from one coil (e.g., resonator coil) to another resonator (e.g., anotherresonator coil) refers to transferring power to do useful work (e.g.,electrical work, mechanical work, etc.) such as powering electronicdevices, vehicles, lighting a light bulb or charging batteries. Bothwireless energy transfer and wireless power transfer refer to thetransfer (or equivalently, the transmission) of energy to provideoperating power that would otherwise be provided through a wiredconnection to a power source, such as a connection to a main voltagesource. Accordingly, with the above understanding, the expressions“wireless energy transfer” and “wireless power transfer” are usedinterchangeably in this disclosure. It is also understood that,“wireless power transfer” and “wireless energy transfer” can beaccompanied by the transfer of information; that is, information can betransferred via an electromagnetic signal along with the energy or powerto do useful work.

Multiple-Element Magnetic Components

FIG. 2 is a schematic diagram of an example of a power transmittingapparatus 102 including a coil 210, a magnetic component 220 and ashield 229 according to coordinate 291. The coil 210 includes aplurality of loops and can be connected to a capacitor (not shown). Thecoil 210 can be formed of a first conductive material. In someembodiments, the coil 210 can be a litz wire. For example, litz wire canbe used for operation frequencies of lower than 1 MHz. In certainembodiments, the coil 210 can be a solid core wire or conducting layers(e.g., copper layers) in a printed circuit board (PCB). For example,such solid core wire or conducting layers can be used for operationfrequencies of 1 MHz or higher. The magnetic component 220 is positionedbetween the coil 210 and the shield 229. The magnetic component 220 canguide a magnetic flux induced by the plurality of loops of the coil 210.The presence of the magnetic component 220 can lead to an increase of amagnetic flux density generated by the coil 210 in a region adjacent tothe coil 210 when oscillating electrical currents circulate in the coil210, compared to the case without the magnetic component 220.

The shield 229 (e.g., a sheet of electrically conductive material) canbe positioned adjacent to the source resonator. The shield 229 can beformed of a second conductive material. For example, the shield 229 canbe formed from a sheet of material such as copper, silver, gold, iron,steel, nickel and/or aluminum. Typically, the shield 229 acts to shieldthe resonator from loss-inducing objects (e.g., metallic objects).Further, in some embodiments, the shield 229 can increase coupling ofthe source resonator to another resonator by guiding magnetic fieldlines in the vicinity of the source resonator. For example, energy lossfrom aberrant coupling to loss-inducing objects can be reduced by usingthe shield 229 to guide magnetic field lines away from the loss-inducingobjects.

While FIG. 2 shows power transmitting apparatus 102, it should beunderstood that a power receiving apparatus (e.g., power receivingapparatus 104 in FIG. 1) or power repeating apparatus can includesimilar elements. For example, power receiving apparatus 104 can includea coil, a capacitor and a magnetic component. A shield can be positionedadjacent to these elements.

Magnetic components can include magnetic materials. Typical magneticmaterials that are used in the magnetic components disclosed hereininclude materials such as manganese-zinc (MnZn) and nickel-zinc (NiZn)ferrites. MnZn based ferrites can include a Mn_(x)Zn_(1-x)Fe₂O₄ where xranges from 0.1-0.9. For example, x can be 0.2-0.8. NiZn based ferritescan include a Ni_(x)Zn_(1-z)Fe₂O₄ ferrite where x ranges from 0.1-0.9.For example, x can be in a range of 0.3-0.4. In some embodiments,magnetic materials can include NiZn based ferrites such as NL12® fromHitachi and 4F1® from Ferroxcube, for example, for operation frequenciesof 2.5 MHz or above. In certain embodiments, magnetic materials caninclude MnZn based ferrites such as ML90S® from Hitachi, for example,for operation frequencies between 500 kHz and 2.5 MHz. In someembodiments, magnetic materials can include MnZn based ferrites such asPC95® from TDK, N95®, N49® from EPCOS and ML24D® from Hitachi, forexample, for operation frequencies of 500 kHz or lower. In certainembodiments, magnetic materials can include amorphous cobalt-basedalloys and nanocrystalline alloys, for example, for operationfrequencies of 100 kHz or lower. Nanocrystalline alloys can be formed ona basis of Fe, Si and B with additions of Nb and Cu. Nanocrystallinemagnetic materials can be an alloy of Fe, Cu, Nb, Si and B (e.g.,Fe_(73.5)Cu₁Nb₃Si_(15.5)B₇). In some embodiments, nanocrystallinemagnetic materials can be an alloy of Fe, Co, Zr, B and Cu. In certainembodiments, nanocrystalline magnetic materials can be an alloy of Fe,Si, B, Cu and Nb. In certain embodiments, nanocrystalline magneticmaterials can be an alloy of Fe, Co, Cu, Nb, Si and B. Thenanocrystalline magnetic materials can include an alloy based on Fe. Forexample, the alloy can be a FeSiB alloy.

While these materials are generally available in small sizes, someapplications for wireless power transfer utilize magnetic componentswith a large areal size. For example, a car battery charging applicationmay need to use a large areal size (e.g., 30 cm×30 cm) magneticcomponent to transfer high power of 1 kW or more (e.g., 2 kW or more, 3kW or more, 5 kW or more, 6 kW or more).

In some embodiments, a single monolithic piece of magnetic componentscan be utiltized when the single monolithic piece of the required sizeis available. In some embodiments, it can be difficult and/or expensiveto manufacture a monolithic piece of magnetic component such as MnZn orNiZn ferrites with a large areal size (e.g., 30 cm×30 cm) needed for thehigh power transfer. Moreover, MnZn and NiZn ferrites can be brittle,and accordingly, large-area pieces of these materials can be highlysusceptible to breakage. To overcome such difficulties when fabricatingthe magnetic components disclosed herein, ferrite materials can bemanufactured in pieces of small areal size (e.g., 5 cm×5 cm), andseveral such pieces can be joined together to form a larger combinedmagnetic component. These smaller magnetic elements can behavefunctionally in a very similar manner as a larger magnetic element whenthey are joined.

However, joining multiple smaller magnetic elements to form a largermagnetic component can introduce gaps and certain inhomogeneitiesrelative to a single sheet of magnetic component. In particular,irregularities at the edges of the small pieces can lead to “magneticfield hot spots,” where magnetic fields are locally concentrated at theirregularities. Magnetic field hot spots due to irregularities at theedges of the joined pieces of magnetic component can damage the magneticcomponent due to heating, and/or reduce the quality factor of theapparatus.

In some embodiments, a gap can be formed between two pieces of magneticelements. The gap can be an air gap, or can be filled with a dielectricmaterial such as adhesive or a type of material different from thematerial of the magnetic elements (e.g., ferrite). When magnetic fieldsoscillate substantially perpendicular to interfaces of the gap, themagnetic fields can be concentrated with high density within the gap. Inaddition, magnetic fields can also be concentrated with high density atlocations above or below the gap, and these concentrated magnetic fieldscan penetrate a portion of a shield at positions above or below or inthe general vicinity of the gap. Such penetration can lead to loss ofenergy by generating eddy currents and heat in the correspondingportions of the shield. Similarly, strongly localized magnetic field hotspots induced by irregularities in the magnetic component may penetratethe shield and lead to loss of energy. To illustrate this phenomena,FIG. 3 is a schematic diagram showing a cross-sectional view of thepower transmitting apparatus 102 shown in FIG. 2 according to coordinate392. In this example, when coil 210 generates a magnetic field within agap 302 of magnetic component 220, portions of the magnetic field 304extend below the gap 302 and penetrate the shield 229, which leads toenergy loss as discussed above.

To mitigate such energy losses, this disclosure features shieldgeometries that reduce the effects of hot spots and concentratedmagnetic fields due to irregularities at the edges and gaps of joinedmagnetic elements (e.g., pieces of magnetic component). In particular,energy losses due to the penetration of magnetic fields into shield 229can be reduced by forming openings in the shield 229 and/or by modifyingthe shape of shield 229 in regions where the magnetic field density islocally increased, e.g., in regions corresponding to gaps between themagnetic elements. By adjusting the shape of the shield 229, the extentto which the magnetic field 304 penetrates the shield 229 can bereduced, thereby mitigating energy losses.

The shields disclosed herein allow the use of magnetic components oflarge areal sizes (e.g., by joining many smaller pieces of magneticcomponent) while reducing energy losses due to interactions between theshield and concentrated magnetic fields. As a result, apparatuses thatinclude the shields disclosed herein can achieve high power transferefficiencies and can operate over a wide range of power transfer levels(e.g., between 0.5 kW to 50 kW). For example, the power transfer can be3.3 kW or more (e.g., 6.6. kW or more).

Shield Configurations

FIG. 4A is a schematic diagram showing an example of a powertransmitting apparatus 102 including a coil 210, a magnetic component220 and a shield 230. Shield 230 can function in a manner similar toshield 229 in FIG. 2, and the shield 230 can include an opening 560which will be described later. Shield 230 can be formed of a conductivematerial similar to shield 229. Coordinate 390 is the local coordinateof the magnetic component 220.

In FIG. 4A, the coil 210 is positioned above the magnetic component 220.The magnetic component 220 is positioned above the shield 230 in theC-direction without a portion of the coil 210 in between the magneticcomponent 220 and the shield 230 (e.g., without coil 210 extending inthe C-direction). This configuration of the coil 210 can provide acompact power transmitting apparatus because the coil 210 does not takeup space between the magnetic component 220 and the shield 230 ascompared to FIG. 22 described later.

The shield 230 lies in a plane nominally parallel to another plane inwhich the coil 210 lies. In this example, the magnetic component 220lies in a plane parallel to another plane in which the coil 210 lies. Incertain embodiments, the magnetic component 220 lies in a planesubstantially parallel (e.g., within 3°, within 5°, within 10°, within15°) to another plane in which the coil 210 lies.

The magnetic component 220 includes four magnetic elements 410, 412, 414and 416 (e.g., ferrite tiles) each shaped as a rectangular slab. Themagnetic elements are joined together with a dielectric material 420 toform the magnetic component 220, which extends in a plane parallel tothe A-B plane. In this example, the dielectric material 420 is anadhesive material which bonds the four magnetic elements 410, 412, 414and 416 together. As explained previously, by fabricating a magneticcomponent from smaller magnetic elements, large-size magnetic componentscan be produced more easily and at lower cost compared to fabricationmethods that rely on producing monolithic elements. By using multiplesmall magnetic elements to form a larger magnetic component, the size ofthe magnetic component can generally be selected as desired for aparticular apparatus. In some embodiments, the size of the magneticcomponent can have an area of 30 cm×30 cm or larger (e.g., 40 cm×40 cmor larger, 50 cm×50 cm or larger).

In some embodiments, the magnetic component 220 can be formed from aplurality of tiles, blocks, or pieces of magnetic component that arearranged together to form magnetic component 220. The plurality oftiles, blocks, or pieces can all be formed from the same type ofmagnetic component, or can be formed from two or more different types ofmagnetic components. For example, in some embodiments, materials withdifferent magnetic permeability can be located at different positions ofthe magnetic component 220. A dielectric material such as adhesive canbe used to glue the different magnetic elements together. In someembodiments, magnetic elements can be in direct contact with oneanother. Irregularities in interfaces between the direct contact canlead to magnetic field hot spots. In some embodiments, the magneticcomponent 220 can include electrical insulator layers, coatings, strips,adhesives for mitigating build-up of heat at irregular interfaces withinthe magnetic component 220.

Referring back to FIG. 4A, the magnetic component 220 includes gaps 422and 423, which are formed between the magnetic elements 410, 412, 414and 416. The discontinuities in the magnetic component 220 betweenadjacent magnetic elements define the gaps 422 and 423. The gap 422 hasits longest dimension extending in the A-direction and a maximum width424 measured in a direction parallel to the B-direction. The gap 423 hasits longest dimension extending in the B-direction and a maximum width425 measured in the A-direction. The dielectric material 420 can fillthe gaps 422 and 423. In some embodiments, the gap 422 has a constantwidth measured in the B-direction. In certain embodiments, the gap 422can have a non-constant width measured in the B-direction, e.g.,depending upon the shapes of magnetic elements 410, 412, 414, and 416.For example, the magnetic elements can be arranged so that the gap 422has a varying width. In some embodiments, the non-constant width can bedue to curved edges of the magnetic elements.

The coil 210 has a plurality of loops which lie in the A-B plane, andincludes windings 451 and 452. The windings 451 and 552 correspond tofirst and second plurality of loops, respectively of the coil 210. Thewinding 451 has an end 401 and connects to the winding 452, which has anend 403. In this example, starting from the end 401, the winding 451 isconcentrically wound around an axis 402 (starting from the inner windingof winding 452 towards its outer winding), which points into the drawingplane in (i.e., negative C-direction in FIG. 4A) according to theright-hand rule convention, which is used through-out this disclosure.The C-direction is perpendicular to the A-direction and the B-direction.As starting from the connected part between windings 451 and 452, thewinding 452 is concentrically wound around an axis 404 (starting fromthe outer winding of winding 452 towards its inner winding), whichpoints out of the drawing plane (i.e., positive C-direction in FIG. 4A).In this example, the winding 451 is wound around in opposite directionof the winding 452 when measured from end 401 to end 403. Dashed arrows479 depict the direction of current flow in the windings 451 and 452 ata given time. In another way to described the winding directions, thewinding 451 can be said to have clock-wise winding starting from itsinner winding as seen towards the negative C-direction from the positiveC-direction, and the winding 451 can be said to have clock-wise windingstarting from its inner winding as seen towards the negative C-directionfrom the positive C-direction. In other words, the two windings can besaid to have the same winding directions when measured from starting attheir respective inner winding towards their outer windings.

The coil 210 is configured to generate oscillating magnetic fields andmagnetic dipoles in the magnetic component 220, which oscillatesubstantially along the B-axis, when currents oscillate within the coil210. The plurality of loops of the coil 210 define a coil that ispositioned in the A-B plane. More generally, the coil 210 may form aflat portion of the coil 210 that is oriented at an angle to the A-Bplane. For example, the angle can be within 5° or less (e.g., 10° orless, 15° or less, 20° or less). Generally, either or both of the axes402 and 404 may point at an angle with respect to the C-direction. Forexample, the angle can be within 5° or less (e.g., 10° or less, 15° orless, 20° or less). In this disclosure, the “x” notation (e.g., of axis402) refers to a direction pointing into the drawing plane (i.e.,negative C-direction in FIG. 4A) and the “dot” notation (e.g., of axis404) refers to a direction pointing out of the drawing plane (i.e.,positive C-direction in FIG. 4A).

In this disclosure an “average magnetic field” of a magnetic componentat a given time refers to the magnetic field integrated over the totalvolume of all magnetic elements in the magnetic component at the giventime. Referring back to FIG. 4A, when an electrical current flowsthrough the coil 210 from the end 403 to the end 401, the current in thewinding 451 circulates counter-clockwise, while current in the winding452 circulates clockwise, as viewed from the positive C-directiontowards the negative C-direction.

The oscillating electrical current in the coil 210 generates magneticfields within the magnetic component 220. To illustrate this, the powertransmitting apparatus 102 shown in FIG. 4A is depicted in FIG. 4B. Thecoil 210 and the shield 230 are not shown. Coordinate 390 is the localcoordinate of the magnetic component 220. Magnetic fields at severallocations of the magnetic elements 410, 412, 414 and 416 at a particulartime are schematically drawn as magnetic field lines 470. FIG. 4B alsoschematically depicts an average magnetic field 471 of the magneticcomponent 220, which is the average of magnetic fields within the volumeof magnetic elements 410, 412, 414 and 416 at a given time. In thisexample, the average magnetic field 471 points in direction 441 alongthe negative B-direction, at a given time. More generally, in someembodiments, the average magnetic field 471 points substantially alongthe direction 441 within 1° (e.g., within 3°, within 5°, within 10°) ata given time. Furthermore, the magnetic fields generated in the gap 422oscillate in the B-direction. Accordingly, the magnetic fields generatedin the gap 422 oscillate in a direction nominally perpendicular to aninterface 432 between the magnetic element 410 and the dielectricmaterial 420 and an interface 434 between the magnetic element 416 andthe dielectric material 420. Direction 442 is perpendicular to thedirection 441.

Generally, when the coil 210 generates magnetic fields in the magneticcomponent 220 with the average magnetic field 471 pointing along thedirection 441 at a given time, high densities of magnetic fields becomeconcentrated in the gap 422. Moreover, irregularities at interfaces 432and 434 of the gap 422 can contribute to form magnetic field hot spots.

FIG. 5 is a schematic diagram of a portion of the power transmittingapparatus 102 shown in FIGS. 4A and 4B, showing the gap 422 betweenmagnetic elements 410 and 416 at higher magnification. Coordinate 390 isthe local coordinate as shown in FIGS. 4A and 4B. The interfaces 432 and434 between the magnetic elements 410 and 416 are also shown. Theinterfaces 432 and 434 form the discontinuities of the magneticcomponent 220 between adjacent magnetic elements 410 and 416. Duringoperation, the coil 210 can generate oscillating magnetic fields, with ahigh density of magnetic fields 521 being concentrated in the gap 422between the interfaces 432 and 434. The gap 422 is filled with thedielectric material 420 (not shown) such as adhesive for joining themagnetic elements 410 and 416. In some embodiments, the gap 422 isfilled with air—in this case, the gap 422 is referred as an air gap.

In some embodiments, strongly localized magnetic field hot spots can beformed within the gap 422. For example, as shown in FIG. 5, interfaces432 and 434 may not be perfectly planar, and may include local peaks(e.g., peak 512 of interface 432) and/or valleys (e.g., valley 514 ofinterface 434). Oscillating magnetic fields between the interfaces 432and 434 along the direction 441 can form “magnetic field hot spots,”where the magnetic fields are locally (e.g., in regions of the peaks orvalleys) concentrated compared to other regions of the interfaces 432and 434.

For example, magnetic fields 520 depicted as dashed arrows within region510 concentrate on the peak 512. Concentrated field regions (e.g.,region 510) may lead to increased heating, material breakdown, and/ordamaging of the magnetic component, which can lead to deteriorated powertransfer efficiency provided by the power transmitting apparatus 102.

Magnetic field hot spots can become more pronounced when the distancebetween the interfaces 432 and 434 is decreased. The distance betweenthe interfaces 432 and 434 can be reduced (for example, when elements410 and 416 are joined together more closely) to achieve a more compactarrangement of the magnetic elements 410 and 416. Polishing theinterfaces can, in certain embodiments, assist in reducing the extent ofirregularities at the surfaces. However, it has generally been foundthat mechanical polishing alone does not fully ameliorate surfaceirregularities that lead to magnetic hot spots.

FIG. 6 is a schematic diagram of a cross-sectional view of the powertransmitting apparatus 102 described in FIGS. 4A, 4B and 5. Coordinate392 is the local coordinate of the magnetic component 220 as shown inFIGS. 4A, 4B and 5. The coil 210 can generate magnetic fields 521 in thegap 422 between the interfaces 432 and 434. In addition, concentratedmagnetic fields 525 are also generated above and below gap 422 due tofringe effects. The fringe effects arise due to the edges of themagnetic elements 410 and 412 at the gap 422, where the edges inducemagnetic fields 525 to curve outwards from the A-B plane of the magneticelements in FIG. 6. In addition, similarly, locations which formmagnetic field hot spots such as in region 510 (shown in FIG. 5) canlead to high magnetic fields above and below the gap 522 due to fringeeffects.

In the examples shown in FIGS. 4A, 4B, 5 and 6, the shield 230 is placedadjacent to the magnetic component 420. This is illustrated in FIG. 6,where the shield 230 is depicted below the magnetic elements 410 and416. The shield 230 includes an opening 560 adjacent to the gap 422.Opening 560 extends entirely through the thickness 611 of shield 230.

For a conventional shield without opening 560, the magnetic fields 525below the gap 422 would penetrate the shield. Because the magneticfields 525 can be strong due to the gap as described above, suchpenetration can induce large eddy currents which can generate heat inthe shield. This leads to energy losses in the power transmittingapparatus 102. If the conventional shield were moved closer to the gap422, the losses become even larger as magnetic fields 525 inducestronger eddy currents in the shield.

However, unlike conventional shields, the shield 230 has its opening 560aligned to the gap between magnetic elements 410 and 416 and located ina region of the magnetic fields 525. As a result, the penetration offields 525 into shield 230 is significantly reduced or even eliminated,thereby mitigating the generation of strong eddy currents in the shield230. Thus, energy losses due to the shield 230 can be reduced or eveneliminated, relative to energy losses that would otherwise occur due toa conventional shield.

Electromagnetic simulations can be used to predict and to comparecharacteristics of various power transmitting apparatuses. FIGS. 7A-Cshow schematic diagrams of a plurality of different embodiments forwhich operating characteristics have been both simulated and measured.FIG. 7A shows a portion of a power transmitting apparatus 700 includinga coil 210. FIG. 7B shows a portion of a power transmitting apparatus710 including a coil 210 and a magnetic component 220. FIG. 7C shows aportion of a power transmitting apparatus 720 including a coil 210,magnetic component 220 and a shield 229. FIGS. 7A-C are depictedaccording to coordinates 291. In all three apparatuses, coil 210includes a litz wire forming a plurality of loops. In apparatuses 710and 720, magnetic component 220 includes a 2×2 array of 100 mm×100 mmN95 ferrite tiles. The N95 ferrite tiles are formed from MnZn ferritematerials. In apparatus 720, shield 229 is 0.3 m×0.3 m in size and doesnot have an opening. The minimum distance between any point on thesurface of magnetic component 220 and any point on the surface of shield229 is 1 mm. FIG. 7D is a schematic diagram of the magnetic component220 in apparatuses 710 and 720. In these embodiments, the magneticcomponent 220 has a constant width 424 of gap 422 measured in theB-direction.

Typically, wireless power transfer using high Q-factor resonators can beefficient because the high Q-factor can lead to large energy transferefficiency between resonators. Furthermore, quality factor Q_(trans) ofan apparatus and quality factor contributed by a shield Q_(shield)(which will be described in greater detail in a later section) can beindicators of how efficient the power transfer can be betweenapparatuses. In the following, the quality factor Q_(trans) of anapparatus and the quality factor contributed by a shield to anapparatus, Q_(shield), are discussed. A smaller value of quality factorQ_(trans) can lead to smaller energy transfer efficiency betweenapparatuses.

FIG. 8 is a plot 800 showing measured and simulated quality factorvalues of apparatuses 700, 710 and 720 as function of an operatingfrequency of currents applied to coil 210, where width 424 of gap 422 is1 mm. Curves 802 and 804 are the measured and simulated quality factorvalues for apparatus 700, respectively. Curves 806 and 808 are themeasured and simulated quality factor values for apparatus 710,respectively. Curves 810 and 812 are the measured and simulated qualityfactor values for apparatus 720, respectively. Curves 810 and 812indicate smaller quality factor values compared to the quality factorvalues of curves 802, 804, 806 and 808 for a given operating frequency.The smaller values are attributable to the presence of the shield 229 ofapparatus 720; energy loss occurs when magnetic fields generated by coil210 penetrate the shield 229, as described in relation to FIGS. 3 and 6.The measured and simulated inductance values of apparatus 700 are 19.2μH and 19.6 μH, respectively. The measured and simulated inductancevalues of apparatus 710 are 26.9 μH and 27.3 μH, respectively. Themeasured and simulated inductance values of apparatus 720 are 26.1 μHand 26.2 μH, respectively.

Electromagnetic simulations can be used to compare characteristics ofsystems with different distances between magnetic component and shields.Generally, the minimum distance between any point on the surface ofmagnetic component 220 and any point on the surface of shield 229 can be1 mm or less (e.g., 2 mm or less, 5 mm or less, 10 mm or less, 15 mm orless, 20 mm or less). FIG. 9 is a plot 900 showing simulated values ofQ_(shield) according to Eq. (3) (described later) of the apparatus 720for different separation distances between the magnetic component 220and the shield 229 in the C-direction at an operating frequency of 85kHz. Q_(shield) is calculated as a function of the width 424 of gap 422measured in the B-direction. Curve 902 corresponds to a zero separationdistance. Curve 904 corresponds to a separation distance of 0.5 mm.Curve 906 corresponds to a separation distance of 1 mm. Curve 902 hasthe smallest Q_(shield) for a given width 424 of the gap 422.Accordingly, shield 229 corresponding to curve 902 leads to the largestenergy loss compared to that of other curves. This is because, for thecase of curve 902, shield 429 is closest to the magnetic component 220,and thus a larger portion of magnetic fields penetrate the shield 229.For all three curves 902, 904 and 906, Q_(shield) decreases as the widthof the gap 422 increases. In some embodiments, a separation distancebetween a shield and a magnetic component can be increased to have ahigher Q_(shield) by reducing penetration of localized magnetic fieldsinto the shield. However, this approach may be disadvantageous becausethe overall size of a power transmitting apparatus becomes larger due tothe increased separation between the shield and the magnetic component.

As previously described, energy loss due to penetration of magneticfields into shield 229 can be reduced by forming openings in the shield229 where the magnetic field density is locally increased, e.g., inregions corresponding to gaps between the magnetic elements. FIG. 10Ashows a cross-sectional view of apparatus 720 according to coordinate392. FIG. 10B shows a cross-sectional view of a power transmittingapparatus 1000, which includes a shield 230 according to coordinate 392.The shield 230 includes an opening 560, which extends along theA-direction and has a maximum width 1009 measured in a directionparallel to the B-direction.

In the example shown in FIG. 10B, the magnetic component 220 extends ina plane in which arrow of direction 441 lies on and parallel to the A-Bplane. Accordingly, the plane extends in the A-direction and theB-direction, which are orthogonal to each other. The plane passesthrough the middle of the magnetic component 220 as measured in theC-direction. The coil 210 is positioned on a first side of the plane inthe positive C-direction. The shield 230 is positioned on a second sideof the plane in the negative C-direction. In this example, the coil 210is positioned entirely on the first side of the plane. In otherexamples, the coil 210 can be at least in part positioned on the firstside of the plane. As described below, the shield 230 can include one ormore openings (e.g., 560) positioned relative to one or more gaps (e.g.,gap 422). The shield 230 can lie in a plane substantially parallel(e.g., within 3°, within 5°, within 10°, within 15°) to the plane inwhich the magnetic component 220 extends. Similar descriptions can beapplied to other examples in this disclosure.

When coil 210 generates a magnetic field within gap 422 of the magneticcomponent 220 in a direction parallel to the B-direction, a portion ofthe magnetic field 525 extends below gap 422 and penetrates shield 229,which leads to energy loss, as discussed previously. The penetration ofportion 525 of the magnetic field into shield 229 is shown on FIG. 10A.

In apparatus 1000, however, penetration of magnetic field 525 intoshield 230 is reduced or eliminated because opening 560 is aligned withgap 422, and therefore positioned at the location where magnetic field525 extends below gap 422. Because there is no shield material wheremagnetic field 525 extends below the gap 422, the effect of magneticfield 525 on shield 230 is significantly mitigated relative to apparatus720.

In general, the opening 560 can be located where the magnetic fieldbelow the magnetic component 420 is particularly strong due to fringeeffects or hot spots. By providing an opening in a region of the shieldwhere strong magnetic fields would otherwise penetrate the shield,energy losses due to the shield can be reduced or eliminated.Accordingly, one or more openings of the shield 230 can be respectivelyaligned with corresponding ones of the one or more gaps of the magneticcomponent 220. The relative positioning of the one or more openings withrespect to the one or more gaps can reduce interactions between magneticflux of the magnetic fields crossing discontinuities of the magneticcomponent 220 and the shield 230. Moreover, the absence of shieldmaterial can lead to a lighter weight shield and reduce shield materialcosts.

In FIG. 10B, opening 560 has the width 1009 and the opening 560 extendsin the A-direction, e.g., out of the plane of FIG. 10B. Typically, dueto the shapes of the magnetic elements and the gaps between them, theopening 560 has a longest dimension extending along the A-direction. Insome embodiments, the longest dimension of the opening 560 issubstantially parallel (e.g., within 3°, within 5°) to the A-direction.In the example shown in FIG. 10B, the width 1009 of opening 560 isorthogonal to its longest dimension, and the width 424 of the gap 422measured in the B-direction is orthogonal to its longest dimensionextending in the A-direction.

The width 1009 of opening 560 of shield 230 can be selected to providereduced energy loss due to magnetic field penetration into the shield230, while at the same time shield 230 still effectively shieldsmagnetic fields from lossy objects. FIG. 11A is a schematic diagram of aportion of a power transmitting apparatus 1100 with an opening 560having a width 1009 of 4 mm in direction 441, which is oriented in adirection parallel to the B-direction of coordinate 1191. FIG. 11B is aschematic diagram of a portion of a power transmitting apparatus 1110with an opening 560 having a width 1009 of 10 mm in direction 441,according to coordinate 1191. Apparatuses 1100 and 1110 each include amagnetic component 220 with a gap 422 (not shown). The gap 422 has awidth 424 in the B-direction.

FIG. 12 is a plot 1200 showing simulated values of Q_(shield) (describedlater) for apparatuses 720 (curve 1202), 1100 (curve 1204) and 1110(curve 1206) at an operating frequency of 85 kHz for currents applied tocoil 210. Q_(shield) is calculated as a function of the width of gap 422measured in the B-direction in mm. Curve 1202 has the smallestQ_(shield) for a given width of gap 422 because, for apparatus 720,penetration by magnetic field 525 into shield 229 occurs to a largerextent than for apparatuses 1100 and 1110 due to the absence of anopening in shield 229. For all three apparatuses 720, 1100, and 1110,Q_(shield) decreases as the width of gap 422 of magnetic component 220increases.

Generally, an opening 560 can have a width 1009 in a direction parallelto oscillations of magnetic fields within a gap of a magnetic component220. Referring back to FIG. 12, plot 1200 shows that apparatus 1110 hasa larger Q_(shield) than that of apparatus 1100 for a given width 424 ofgap 422. Accordingly, in some embodiments, it can be advantageous tohave an opening 560 with a width 1009 larger than width 424 of the gap422. This is because with a larger width 1009, penetration of locallyconcentrated magnetic fields within the gap 422 into shield 230 isreduced.

In certain embodiments, a ratio of the width 1009 to width 424 can be10:5 or less (e.g., 10:2.5 or less, 10:2 or less, 10:1 or less, 10:0.5or less, 10:0.4 or less, 10:0.2 or less). A high ratio may lead to ahigher Q_(shield). In some cases, if the ratio of the width 1009 towidth 424 is too large, the shield 230 may not effectively shield lossyobjects. In some embodiments, the ratio of the width 1009 to width 424is not larger than 100:1 (e.g., not larger than 50:1, not larger than25:1). For example, the ratio of the width 1009 to width 424 can beabout 100:1 rather than 25:1 when the width 424 is smaller compared tothe case when it is larger.

In some embodiments, gap 422 can have a minimum width of 0.2 mm or more(e.g., 0.5 mm or more, 1 mm or more, 1.5 mm or more, 2 mm or more).Opening 560 can have a minimum width of 1 mm or more (e.g., 2 mm ormore, 4 mm or more, 8 mm or more, 10 mm or more, 15 mm or more).

In some embodiments, width 1009 of opening 560 can be equal to or lessthan width 424 of gap 422. Such a configuration may be utilized, forexample, when a thickness of shield 230 is about a skin depth or less(e.g., half the skin depth) of the shield material and/or one or morelossy objects are close by (e.g., within 3 mm) to the shield 230. Theskin depth of the shield material is the length of material throughwhich the oscillating magnetic fields at the operating frequency passbefore their amplitudes have decayed by a factor 1/e. In this case, ifthe width 1009 is larger than the width 424, concentrated magneticfields within gap 422 can still interact with the lossy object becausethe thickness of shield 230 is relatively thin and/or the lossy objectis close to the shield 230. Therefore, in this case, it can be desirableto have width 1009 to be equal or less than width 424 although magneticfields may still penetrate the shield 230.

In this disclosure, a characteristic size of the magnetic component 220is defined as the radius 1011 of the smallest sphere that fits aroundthe magnetic component 220 as illustrated in FIG. 10C. The extent offringing magnetic field (e.g., field 525) induced in the vicinity of themagnetic component 220 can depend on the characteristic size of themagnetic component 220. For example, if the characteristic size isscaled by a factor of 2, the extent of fringing magnetic field may scaleby a factor of 2. Because of the dependence of the fringing magneticfield on the characteristic size, an optimum width 1009 of opening 560can depend on the characteristic size of the magnetic component 220.When the ratio of the width 1009 to the characteristic size of themagnetic component 220 becomes larger, the fringing magnetic field canmore effectively pass through the opening 560 and interact with a lossyobject, which may be positioned on the other side of the shield 230.Such interaction can lead to losses of magnetic fields induced in thevicinity of the magnetic component 220. Accordingly, in certainembodiments, it is advantageous to have the ratio of the width 1009 tothe characteristic size to be an optimum value or less to avoid thelosses described in the preceding sentence. For example, the ratio ofthe width 1009 to the characteristic size of the magnetic component 220can be 1:10 or less to mitigate the effects of magnetic fields passingthrough opening 560 and interacting with lossy objects. In certainembodiments, the ratio can be 1:12 or less (e.g., 1:15 or less).

Referring to FIG. 11B, the coil 210 is electrically disconnected fromthe shield 230. This approach can lead to easier manufacturing of thearrangement 1110 compared to approaches where a coil is electricallyconnected to a shield. The coil 210 lies above the magnetic component220 without passing through gaps of the magnetic component 220. Thisapproach can lead to easier manufacturing of the arrangement 1110compared to the approach described later in relation to FIG. 22, becausethe coil 210 can be easily positioned above the magnetic component 220.A single power source can be used to drive the coil 210.

Referring back to FIG. 10B, oscillation of currents in coil 210 caninduce “image” currents in shield 230. Such image currents can generallybe described in a manner analogous to image charges and the method ofimages used to replicate electromagnetic boundary conditions along aninfinite plane of a perfect conductor. Image currents can flow in adistribution at the surface of the shield 230 and in some embodiments,the image currents in the shield 230 can increase the effectivethickness of the magnetic component 220 (e.g., by a factor of about 2).In FIG. 10, opening 560 does not significantly disrupt image currentsformed in the shield 230 because the opening 560 extends parallel to theimage currents. For example, referring back to FIG. 4A, center portion440 of coil 210 has currents flowing in positive and negative directionsof axis A at a given time. Accordingly, in a shield positioned adjacentto center portion 440, image currents flow in both the positive andnegative A-directions as well. When opening 560 extends along theA-direction, the opening 560 does not extend perpendicular to imagecurrents below the center portion 440, but instead extends parallel tothe image currents. Accordingly, opening 560 does not significantlydisrupt the image currents in the shield 230.

FIG. 13A is a schematic diagram of a power transmitting apparatus 1300without a shield placed between a magnetic component 220 and a lossyobject 1302 according to coordinate 1391. Direction 441 points in thenegative B-direction. FIG. 13B is a schematic diagram of a powertransmitting apparatus 1310 including a shield 230 (e.g., a coppershield) with an opening 560, positioned between a magnetic component 220and a lossy object 1302, according to coordinate 1391. Direction 441points in the negative B-direction. The shield 230 is separated from thelossy object 1302 by a distance of 2.5 mm in the C-direction. Magneticcomponent 220 is formed from a 2×2 array of magnetic elements joined bydielectric material 420, which fills the gaps between the magneticelements, in the same manner as described previously. Dielectricmaterial 420 is not depicted in FIGS. 13A and 13B. In these examples,the lossy object 1302 formed of ASTM type A1008 steel.

FIG. 14 is a plot 1400 showing simulated values of Q_(shield) (describedlater) for apparatuses 1300 and 1310 at an operating frequency of 85 kHzfor currents applied to coil 210. Q_(shield) was calculated as afunction of width 424 of gap 422 of the magnetic component 420 measuredin direction 441. Curve 1220 corresponds to apparatus 1300 with noshield. Curve 1404 corresponds the apparatus 1310 where the width 1009of opening 560 is 0 mm. Curve 1406 corresponds to apparatus 1310 wherethe width 1009 of opening 560 measured in the direction 441 is 4 mm.Curve 1408 corresponds to apparatus 1310 where the width 1009 of opening560 is 10 mm. Apparatus 1300 has the smallest Q_(shield) due to absenceof a shield. The apparatuses that correspond to openings of width 4 mmand 10 mm have higher Q_(shield) than the apparatus that corresponds tono opening, indicating that the presence of opening 560 can reduce powerdissipation and energy losses induced by the presence of a shield.

As described above, in some embodiments, the width of opening 560 can beselected based on the width of gap 422. To choose the width of opening560, a plot such as plot 1400 can be used. In certain embodiments, wherewidth of gap 422 is fixed, the width of opening 560 can be selected. Forexample, for a width of 0.2 mm of gap 422, the width of opening 560 canbe selected to be 4 mm over 10 mm. For a width of 1.8 mm of gap 422, thewidth of opening 560 can be selected to be 10 mm over 4 mm according toplot 1400. Other widths than 4 mm and 10 mm of opening 560 can beselected to have a higher Q_(shield) depending on a fixed width of gap422.

FIG. 15A shows a series of images of an example of a power transmittingapparatus including a coil 210. Image 1500 shows the coil 210 positionedon one side of a support 1502. Image 1510 shows the other side ofsupport 1502 where a magnetic component 220 is positioned. Image 1520shows a shield 229 without an opening or segments. The shield 229 ispositioned such that magnetic component 220 is positioned between shield229 and support 1502.

FIG. 15B shows a series of images of example of another powertransmitting apparatus including a coil 210. Image 1530 shows a coil 210positioned on one side of a support 1502. A shield 230 with an opening560 is positioned below the support 1502. Image 1540 shows a magneticcomponent 220 a shield 230, which are positioned on the opposite side ofsupport 1502 from the coil 210.

FIG. 16 is a plot 1600 showing measured values of Q_(trans) values forthe apparatuses shown in FIGS. 15A and 15B as a function of operatingfrequencies of currents applied to coil 210. Curve 1602 corresponds tothe apparatus in FIG. 15A with no opening in shield 229. Curve 1604corresponds to the apparatus in FIG. 15B with a shield opening of width2 mm. Curve 1606 corresponds to the apparatus in FIG. 15B with a shieldopening of width 5 mm. Curve 1608 corresponds to the apparatus in FIG.15B with a shield opening of width 10 mm. It is evident from plot 1600that as the width of opening 560 increases, Q_(trans) also increases ateach operating frequency.

FIG. 17 is a plot 1700 showing measured values of Q_(shield) for theapparatuses shown in FIGS. 15A and 15B as a function of the operatingfrequencies of currents applied to coil 210. Curve 1702 corresponds tothe apparatus in FIG. 15A with no opening in shield 481. Curve 1704corresponds to the apparatus in FIG. 15B with a width of 2 mm foropening. Curve 1706 corresponds to the apparatus in FIG. 15B with awidth of 5 mm for opening. Curve 1708 corresponds to the apparatus inFIG. 15B with a width of 10 mm for opening. It is evident from plot 1700that Q_(shield) increases for a given operating frequency as width ofthe opening 560 becomes larger.

Openings in the shield can generally be implemented in a variety ofways. In some embodiments, a shield can be segmented into two pieceslike the example shown in FIG. 15B. In certain embodiments, a shield canbe a monolithic piece of conductor with an opening. To illustrate this,FIG. 18A shows a schematic diagram of a shield 1850 formed of amonolithic piece of conductor with length 1854 measured in theA-direction of coordinate 390. The shield 1850 includes an opening 1852having a length 1856 smaller than the length 1854 in the A-direction.Such a shield 1850 can be fabricated from a single sheet of conductor,where the opening 1852 is drilled, punched, cut, stamped, pressed, orotherwise introduced into shield 1850. Such an approach can beadvantageous due to ease of manufacturing. Further, the use of amonolithic shield can eliminate the alignment of two different pieces ofconductor to form a shield. In this example, the opening 1852 extendsentirely through the thickness of the shield 1850, although moregenerally, opening 1852 can also extend only partially through thethickness of shield 1850. Further, although shield 1850 includes oneopening 1852 in FIG. 18A, more generally shield 1850 can include anynumber of openings.

FIGS. 18B and 18C show schematic diagrams of a shield 1800 with notches1802 and 1803. In FIG. 18B, coordinate 390 indicates the orientation ofthe shield 1800. The notch 1802 can be positioned such that it isaligned with a gap 422 of a magnetic component 220 where magnetic fieldscan be concentrated, as shown in FIG. 18C. Similarly, the shield 1800can be positioned such that notches 1803 are aligned with magnetic fieldhot spots 1806 in the magnetic component 220 (shown in FIG. 18C), whichare described in greater detail above.

FIG. 18C shows a cross-sectional view of the shield 1800 according tocoordinate 392. The notch 1802 extends to a fraction of the thickness1804 of the shield 1800 but sufficiently deep enough to reducepenetration of magnetic field 525 into the shield 1800. For example, adepth 1805 from a surface of the shield 1800 to the deepest point of thenotch 1803 can be about twice or more (e.g., three times or more, fourtimes or more) of a skin depth of the shield material of the shield 1800at the operating frequency. Generally, the shield 1800 can includecurved grooves forming depressions in the shield.

The strength of the magnetic field 525 typically decays away from thesurface of magnetic component 220 according to a power law of the ratio(α) of the width of gap 422 (i.e., width 424 in FIG. 10B) to thedistance of magnetic field 525 from the surface of the magneticcomponent (i.e., the surface facing shield 1800 in FIG. 18C), where thedistance is measured in the −C direction in FIG. 18C. To reducepenetration of the magnetic field into shield 1800, in some embodiments,notch 1802 and/or notch 1803 can extend to a depth below a surface ofthe shield (i.e., below the surface facing magnetic component 220 inFIG. 18C) of 1/α or more (e.g., about 1/2α or more). The cross-sectionalprofile of the notch 1802 can be curved, as shown in the cross-sectionalview, or triangular, as shown for notch 1803. Similarly, thecross-sectional profile for notch 1803 can be triangular, as shown inthe cross-sectional view, or curved as shown for notch 1802.

FIG. 18D is a schematic diagram of a shield 1860 including multipleopenings 1862. In this example, each of the openings 1862 are aligned tomultiple gaps 422 between magnetic elements 1863 to mitigate thepenetration of concentrated magnetic fields into the shield 1860. Eachof the openings 1862 has a width that extends parallel to theB-direction. FIG. 18E is a schematic diagram of a shield 1870 includingopenings 1872 and 1874. The openings 1872 and 1874 have non-rectangularcross-sectional shapes so that the openings 1872 and 1874 are aligned togaps 422 between magnetic elements 1873, 1875 and 1876 to mitigate thepenetration of concentrated magnetic fields into the shield 1870.Generally, openings can have cross-sectional profiles includingtriangular, trapezoidal, circular, elliptical, parabolical andhyperbolical shapes. The profiles can be selected based on geometry ofgaps and arrangements of magnetic elements.

More generally, a magnetic component can be formed in a way thatmultiple gaps exist and magnetic fields oscillate perpendicular tosurfaces of the gap, for example, as described above. In this case,multiple openings and notches can be formed in the shield to reducepower dissipation and energy loss due to the shield positioned below themagnetic component. The openings and notches can form depressions in theshield that extend only partially through a thickness of the shield, orcan extend completely through the shield. In similar manner described inpreceding paragraphs, the depressions can be positioned to berespectively aligned with corresponding gaps of the magnetic component.The depressions can be positioned relative to the gaps to reduceinteractions between magnetic flux of magnetic fields crossingdiscontinuities of the magnetic component and the shield.

In the example shown in FIG. 18D, the shield 1860 has three openings1862. In certain embodiments, the shield 1860 can have other number(e.g., two, four, five) of openings to match a number of gaps 422 formedby magnetic elements. At least one of the gaps 422 can be filled withdielectric material (e.g., adhesive material).

In some embodiments, openings formed in the shield have lateral surfacesthat are orthogonal to the surface of the shield that faces the magneticcomponent. More generally, however, openings formed in the shield canhave lateral surfaces with a variety of orientations with respect to thesurface of the shield that faces the magnetic component. FIG. 18F is aschematic diagram of a cross-sectional view of a shield 1880 accordingto coordinate 392. The shield 1880 includes an opening 1882, whichextends entirely through the shield 1880 of its thickness 1886. In thisexample, the opening 1882 has tapered side-walls. In other words, theside-walls of the opening 1882 form angle 1888 with respect to theC-direction, which is normal to the surface of shield 1880 that facesmagnetic component 220. In some embodiments, the angle 1888 can be 45°or less (e.g., 30° or less, 15° or less). By having a larger open regioncloser to gap 422 of magnetic component 220 and a smaller open region onthe other side of the magnetic component 220, where lossy object 1889 ispositioned, the opening 1882 can mitigate penetration of magnetic field525 into the shield 1880 due to the larger open region, whileeffectively shielding lossy object 1889 due the smaller open region.Similarly, notch 1884 can be aligned to magnetic field hot spot 1806 tomitigate magnetic field penetration into shield 1880. In this example,notch 1884 has cross-sectional profile of a trapezoidal shape.Generally, the profile can be a triangular, trapezoidal, circular,elliptical, parabolical and hyperbolical shapes. The profiles can beselected based on geometry of gaps and arrangements of magneticelements. An opening or notch which forms a depression can have a widthmeasured at the surface of the shield facing the magnetic component tobe larger than a width of the depression measured at another locationbetween its lateral surfaces.

FIG. 18G is a schematic diagram of a cross-sectional view of a shield1895 according to coordinate 392. In this example, opening 1897 ofshield 1895 has one or more curved edges 1896, which are shaped toconform to a distribution of the magnetic field 525 along the negativeC-direction to mitigate penetration of field 525 into the shield 1895.

During use of a power transmitting apparatus, magnetic component 220 canbecome damaged, which may lead to the formation of hot spots. Theexistence and/or development of hot spots can be monitored using athermal detector with appropriate spatial resolution. For example, thethermal detector can measure localized high temperature points which cancorrespond to damage or defects in the magnetic component 220. Thenopenings or notches described in detail above can be formed into ashield based on the monitored hot spots to accommodate the presence ofhot spots.

In some embodiments, the width of gap 422 between elements of themagnetic component can vary, and accordingly, an opening of shield 230can have a varying width to match the varying width of gap 422. Toillustrate this, FIG. 19A shows a schematic diagram of an example of apower transmitting apparatus 1900 according to coordinate 390. Theapparatus 1900 includes a coil 210, a magnetic component 220 and ashield 1920. The magnetic component 220 includes an array of magneticelements 1910. The coil 210 is configured to generate magnetic fieldsoscillating along the B-direction within the magnetic component 220. Themagnetic elements 1910 are positioned between the coil 210 and theshield 1920 along the C-direction. The magnetic elements 1910 aretapered and have side-walls 1911 extending at an angle relative to theA-direction. The angle can be, for example, 45° or less (e.g., 30° orless, 15° or less). The angle of the side-walls with respect to theA-direction produces a gap of varying width in the B-direction betweenelements 1910 of the magnetic component 220 (exaggerated in FIG. 19A forpurposes of illustration).

The varying width of the gap leads to varying magnetic resistance of themagnetic component 220 along the A-direction. Accordingly, when the coil210 generates magnetic field within the magnetic component 220, magneticelements 1910 can be arranged so that the varying magnetic resistanceprovides a more uniform distribution of magnetic fields than wouldotherwise be possible with a gap of constant width in the B-direction,thereby leading to less power dissipation in the magnetic component 220.

For magnetic components with gaps between elements that vary in width,opening 1921 of the shield 1920 can also have varying width to match thevarying width of the gap between magnetic elements 1910 to mitigateconcentration of penetration of magnetic fields into the shield 1920.

FIG. 19B is a schematic diagram of a cross-sectional view of a powertransmitting apparatus 1930, which includes a magnetic component 220 anda shield 230, according to coordinate 392. In this example, the magneticcomponent 220 has curved edges 1932. The curved edges 1932 can lead toreduced fringe effects at gap 422 so that magnetic fields 525 extendless outward of the gap 422 compared to the case shown in FIG. 10B withstraight edges. Thus, in this approach, shield 230 can have an opening560 with smaller width because magnetic field 525 can penetrate lessinto the shield 230 due to reduced fringe effects. In some embodiments,the magnetic component 220 can have beveled edges cut as a straight lineinstead of curved edges. In some embodiments, the shield 230 can havecurved edges 1934 at its opening 560. An opening with curved edges mayreduce concentration of induced eddy currents by magnetic field 525, andthereby reducing losses by the shield 230. In certain embodiments, theshield 230 can have beveled edges cut as a straight line instead ofcurved edges.

FIG. 19C is a schematic diagram of a cross-sectional view of a powertransmitting apparatus 1940, which includes a magnetic component 220 anda shield 230, according to coordinate 392. In this example, a magneticmaterial 1942 fills in gap 422. The magnetic material 1942 can be adifferent type of material from that of magnetic component 220. Forexample, in some embodiments, magnetic material 1942 can have a largermagnetic permeability than that of magnetic component 220. When magneticmaterial 1942 has a larger magnetic permeability than magnetic component220, magnetic fields 525 typically do not extend outward from gap 422 asfar as they would if magnetic material 1942 had a smaller magneticpermeability than magnetic component 220, because the magnetic material1942 helps to confine magnetic fields within the gap 422. In certainembodiments, the magnetic material 1942 can be applied to thoroughlyfill in the gap 422. Thus, in the above approach, shield 230 can have anopening 560 with smaller width because magnetic field 525 penetratesless into the shield 230 due to reduced fringe effects.

FIG. 19D is a schematic diagram of a cross-sectional view of an exampleof a power transmitting apparatus 1950, which includes a magneticcomponent 220 and a shield 230, according to coordinate 392. In thisexample, magnetic tape 1954 is attached over gap 422 in a locationbetween the magnetic component 220 and the shield 230. The magnetic tape1954 can contact the magnetic component 220. Due to the magneticpermeability of the magnetic tape 1954, the magnetic tape 1954 canconfine magnetic fields, mitigating the fringe effect of gap 422. As aresult, magnetic fields 525 do not extend as far outward from gap 422.Thus, in this approach, shield 230 can have an opening 560 with smallerwidth because magnetic field 525 penetrate less into the shield 230 dueto reduced fringe effects attributable to the presence of magnetic tape1954. Material within gap 422 can include dielectric material and/ormagnetic material as described in preceding paragraphs.

In some embodiments, a dielectric material or magnetic material can fillin gap 422 of a magnetic component 220. The dielectric material (e.g.,coolant liquids) or magnetic material filling the gap 422 can have highthermal conductivity and be placed between magnetic elements tofacilitate the dissipation of heat generated within the magneticelements. Referring to FIG. 19E, a magnetic component 220 includes anarray of magnetic elements 1962-1966 according to coordinate 390. Only afew magnetic elements are labeled in FIG. 19E for simplicity. Adielectric material 420 of high thermal conductivity fills in gapsbetween the magnetic elements 1962-1966. Accordingly, heat generated atmagnetic elements 1964 and 1966 in inner regions of the magneticcomponent 220 can effectively transfer to heat sinks 1967 contactingsides of the magnetic component 220. For example, the heat sinks 1967can contain coolant for transferring heat out of the magnetic component220.

In the example shown in FIG. 19E, the array is a 4×4 array. Moregenerally, however, any number of magnetic elements can be joined toform a magnetic component, which allows the size of the magneticcomponent to extend over a larger area than that shown in FIG. 19E.

In some embodiments, magnetic elements can be joined together by anadhesive tape. For example, FIG. 19F is a schematic diagram showing anexample of a magnetic component 220 joined by an adhesive tape 1981within gaps 422 and 423 and sandwiched between magnetic elements 410,412, 414 and 416. As another example, FIG. 19G is a schematic diagramshowing an example of another magnetic component 220 with magneticelements joined together by adhesive tape 1982 and 1983.

FIG. 19H is a schematic diagram of a magnetic component 220 having arectangular cuboid shape with magnetic elements 410, 412, 414 and 416and gaps 422 and 423. Generally, a magnetic component can be in otherforms than a rectangular cuboid. For example, FIG. 19I is a schematicdiagram of an example of a magnetic component 220 of a cylindricalshape. The magnetic component 220 has two magnetic elements 410 and 416with gap 422 in between. As another example, FIG. 19J is a schematicdiagram of another example of a magnetic component 220 of an elongatedcylinder with oval face 1971. The magnetic component 220 includesmagnetic elements 410, 412 and 414 with gaps 422.

In addition to the shield geometries disclosed above for mitigatingenergy losses due to penetration of the magnetic fields from themagnetic component into the shield, other techniques can also be used toreduce energy losses.

In some embodiments, for example, energy losses due to penetratingmagnetic fields can be reduced by adjusting the magnetic fielddistribution within the magnetic component. FIGS. 20A and 20B areschematic diagrams of additional examples of coil 210. Coordinate 390indicates the coordinate axis. A shield is not shown. In the left-handside of FIG. 20A, coil 210 includes a conducting wire forming aplurality of loops, where different portions of the loops correspond todifferent diameters of the wire. For example, portion 2031 of the wirehas a larger diameter than portion 2032. Portion 2032 of the wire has alarger diameter than portion 2033. Differences in diameters in differentportions of the coil are schematically depicted by the thickness oflines of the coil 2030. To illustrate this, a cross-sectional view alongsection line B1-B2 is depicted on the right-hand side of FIG. 20Aaccording to coordinate 392. The variations of diameters along the wiremay be used to control a uniformity of magnetic field distributioninduced in magnetic component 220 by the coil 210. For example, a moreuniform distribution can lead to less hot spots and energy losses of themagnetic fields. In some embodiments, the diameter variation can beselected based on the geometry of magnetic component 220.

FIG. 20B is a schematic diagram of an example of a power transmittingapparatus 2020. A shield is not shown. Two coils 2040 and 2041 arepositioned adjacent to a magnetic component 220. Each of two coils 2040and 2041 includes a plurality of loops. Currents can be separatelyapplied to coils 2040 and 2041 to generate a magnetic field distributionin the magnetic component 220. For example, oscillating currents can beapplied with equal magnitude and phase to coils 2040 and 2041 so that,at a given time, currents within the coil 2040 circulatecounter-clockwise and currents within the coil 2041 circulate clockwiseas seen from the positive C-direction towards the negative C-direction.

The magnitudes and phases of the applied currents in each of the twocoils 2040 and 2041 can be selected to control a uniformity of magneticfield distribution induced in the magnetic component 220. A more uniformdistribution can lead to less hot spots and energy losses of themagnetic fields within the magnetic component 220. In contrast, lessuniform magnetic distribution may localize fields into hot spots. Themagnitudes and phases can be selected depending on the geometry and/orproperties of the magnetic component 220.

Non-uniform magnetic field distributions within the magnetic componentlead to the formation of hot spots, because power is dissipated locallyin proportion to the square of the magnetic field amplitude. Moreover, anon-uniform magnetic field distribution increases the loss coefficientof the magnetic component. Both of these effects lead to a reducedquality factor for a resonator that includes the magnetic component, andcan even cause the magnetic component to saturate at lower power levels.

However, these effects can be mitigated by generating a more uniformmagnetic field distribution within the magnetic component, as describedabove. In particular, because power dissipation varies approximatelyproportionally to the square of the magnetic field amplitude, for afixed total magnetic flux through a magnetic component, a configurationwith a more uniform field distribution will generally exhibit lowerlosses than a configuration with a more non-uniform field distribution.The effect is analogous to the electrical resistance of an electricalconductor, where decreasing the effective cross-sectional area of theconductor leads to higher resistance, for example, due to the skineffect.

In some embodiments, magnetic elements positioned below coil 2040 canhave a different magnetic resistance than the magnetic elementspositioned below coil 2041 due to manufacturing imperfections that leadto different sizes of magnetic elements and/or different magneticpermeabilites of the magnetic elements. For example, magnetic elementspositioned below coil 2040 can have a magnetic permeability smaller by2% or more (e.g., 5% or more, 10% or more) than that of magneticelements positioned below coil 2041 due to fabrication tolerances and/orerrors.

To circumvent such imperfections, coil 2040 can operate with currenthaving a magnitude that is larger by 2% or more (e.g., 5% or more, 10%or more) than that of coil 2041. The phase difference of currentsbetween the coils 2040 and 2041 can be 10° or more (e.g., 20° or more,30° or more) to match a magnitude of the currents at a given time. Suchapproaches may lead to a more uniform magnetic field distribution,thereby reducing the formation of hot spots that lead to magnetic fieldsbending outwards from gaps between the elements of magnetic component220, and also reducing energy losses of the magnetic fields within themagnetic component 220. In some embodiments, either or both of two coils2040 and 2041 can have varying diameters of wire in a similar mannerdescribed in relation to coil 210 in FIG. 20A.

FIG. 21 is a schematic diagram of another example of coil 210.Coordinate 390 indicates the coordinate axis. A shield is not shown. Inthe left-hand side of FIG. 20A, coil 210 includes two windings 451 and452 similar to coil 210 shown in FIG. 4A. But in this example, portionsof windings 451 and 452 have different spacings 2111 and 2112. Forexample, wire portion 2131 of the coil 210 has spacing 2112 from theadjacent wire portion 2132. Wire portion 2134 of the coil 230 hasspacing 2111 from the adjacent wire portion 2133. To illustrate thisfurther, a cross-sectional view along section line B1-B2 is depicted onthe right-hand side of FIG. 21 according to coordinate 392.

By providing a coil with an increased spacing 2111 (e.g., relative tospacing 2112) between adjacent loops in the region of coil 210 that isnear gap 422 (not shown) in the magnetic component, the concentration ofmagnetic fields within gap 422 can be reduced, because less dense coilwindings can induce weaker magnetic fields. Thus, penetration ofmagnetic fields into an adjacent shield can be reduced. Moreover,variations in spacings between adjacent wire portions in coil 210 can beused to control a uniformity of magnetic field distribution induced inmagnetic component 220, leading to less hot spots and energy losses ofthe magnetic fields.

FIG. 22 is a schematic diagram of a power transmitting apparatus 2200,which includes a coil 2204 having a plurality of loops wrapped around amagnetic component 220. In this example, the coil 2204 is connected toat least one capacitor (not shown). The conductor shield 2206 caninclude two flaps 2207 which are bent down ends of the conductor shield2206. The flaps 2207 do not add to the overall length 2209 of theconductor shield 2206, but can improve the shielding effect of theconductor shield 2206 by deflecting and guiding magnetic field linesdownwards, and reducing field interactions with lossy object 2208. Thisconfiguration can increase the effectiveness of conductor shield 2206without increasing its length 2209.

The coil 2204 is wound around the magnetic component 220, which can haveone or more gaps 422 (not shown) as described above. The gaps may leadto concentrated magnetic fields penetrating into the shield 2206.Accordingly, the shield 2206 can have an opening 2210 aligned to a gap422 of the magnetic component 220 to mitigate the magnetic fieldpenetration.

FIG. 23 is a schematic diagram of another example of a powertransmitting apparatus 2300 according to coordinate 2391. The apparatus2300 includes multiple coils 2304, where each coil 2304 is wound arounda magnetic component 2302, with several such magnetic components 2302are arranged as an array. The magnetic component 2302 may or may nothave gaps 422 as described for magnetic component 220. In someembodiments, coil 2304 is in direct contact with it respective magneticcomponent 2302. In certain embodiments, coil 2304 is not in directcontact with it respective magnetic component 2302. The coils 2304 areconfigured to generate oscillating magnetic fields and magnetic dipoleswithin their respective magnetic components 2302 when currents oscillatewithin the coils 2304. For example, at a given time, the coils 2304 cangenerate magnetic dipoles along the axis of dipole moments 2303. Theconfiguration shown in FIG. 23 can be used in preference to an apparatusthat includes a large monolithic magnetic component, for example, with asize of the combined areas of the four magnetic components 2302, due tothe difficulties associated with producing such large magneticcomponents disclosed herein. The configuration may also be advantageousin that multiple larger sized and differently shaped apparatuses can beassembled from smaller and single-sized apparatuses. In somemanufacturing, the ability to assemble, repair and reconfigure a widerange of apparatus configurations from a number of subcomponents thatmay be tracked, stored, shipped can be desirable. The four magneticcomponents 2302 are separated by gaps 2310 and 2311, which correspond toseparations AA and BB, respectively. Accordingly, within the gap 2311,magnetic fields generated by the coils 2304 oscillate in theB-direction.

The apparatus 2300 can include a shield 2320 positioned adjacent to themagnetic component 2302 in the negative C-direction. The shield 2320 caninclude an opening 2322, which can act as an opening 560 describedabove. The configuration of apparatus 2300 can be advantageous becauseeach of the coils 2304 can generate strong magnetic flux densitieswithin respective magnetic components 2302, which can be utilized forproviding for high power transfer in applications such as car charging.

In the example shown in FIG. 23, the magnetic components 2302 extends ina plane in which the arrows of axis of dipole moment 2303 lie on andparallel to the A-B plane. The plane passes through the middle of themagnetic components 2302 as measured in the C-direction. Parts of thecoils 2304 are positioned on a first side of the plane in the positiveC-direction, while the other parts of the coils 2304 are positioned on asecond side of the plane in the negative C-direction. The shield 2320 ispositioned on the second side of the plane in the negative C-direction.Accordingly, the coils 2304 are, in part, positioned on the first sideof the plane. Generally, the shield 2320 can include one or moreopenings (e.g., opening 2322) positioned relative to one or more gapswithin the magnetic components 2302 or between the magnetic components(e.g., gap 2311). Similar description can be applied to the examplesshown in FIGS. 22 and 24A.

FIG. 24A is a schematic diagram of a power transmitting apparatus 2400including a plurality of conducting wire segments 2432 that form a coil,and a shield 2481 electrically connected to the plurality of conductingwire segments 2432, according to coordinate 2491. In this example, amagnetic component 220 is disposed in an internal region of the coildefined by the conducting wire segments 2432 and the shield 2481. Theshield 2481 is split into distinct isolated conductor segments 2402 eachelectrically connected to different conducting wire segments 2432. Thenet result is a series connection of conductor wire segments 2432alternated with electrically isolated segments of the shield 2481. Theisolated segments of the shield 2481 can be electrically insulated fromone another by air gaps or by one or more dielectric materials withhigh-breakdown voltages, such as Teflon, Kapton, and/or pottingcompound. In certain embodiments, the conductor wire segments 2432 canbe electrically isolated from one another. Electrical currents cantherefore be applied independently to each of the conducting wiresegments 2432.

The configuration of apparatus 2400 can eliminate a portion of the wiresthat might otherwise be positioned between the magnetic component andthe shield (as shown in FIGS. 22 and 23, for example). To illustratethis, FIG. 24B shows a schematic diagram of a cross-sectional view ofthe apparatus 2400 according to coordinate 2492. The conducting wiresegments 2432 are electrically connected to the shield 2481 with theabsence of wire portions below the magnetic component 220 in thenegative C-direction (i.e., between magnetic component 220 and shield2481). This configuration can lead to a lighter weight and more compactapparatus due to the absence of the wire portions.

Referring again to FIG. 24A, the magnetic component 220 can include gaps422 between magnetic elements (not shown in FIG. 24A). The coil segments2432 can generate magnetic fields oscillating in the B-direction withinthe gaps 422. Accordingly, shield 2481 can include openings of the typedescribed herein to reduce the penetration of magnetic fields in the gapregions into the shield. To illustrate this, FIG. 24C shows the shield2481 viewed in the positive C-direction according to coordinate 2493.Dashed line 2483 corresponds to the magnetic component 220 shown in FIG.24A.

The shield 2481 includes multiple openings 560 which are aligned torespective gaps 422 depicted in FIG. 24A. Gap 422 at the center of themagnetic component 220 is not shown in FIG. 24A. Accordingly, similar toother embodiments, the shield 2481 can have one or more openings ornotches aligned to gaps or hot spots in the magnetic component 220 toreduce or eliminate power dissipation and energy losses in the shield2481 by penetrating magnetic fields.

The disclosed techniques can be implemented during a manufacturingprocess of an apparatus (e.g., power transmitting apparatus, powerreceiving apparatus, power repeating apparatus) utilized in a wirelesspower transfer system. For example, the type of magnetic elements andarrangement can be selected to form a magnetic component. Thearrangement defines the location and positions of gaps between themagnetic elements. In some embodiments, the shape and position of one ormore coils with respect to the magnetic component can be determined.During manufacture, currents are directed through the one or more coils,and the temperature distribution of the magnetic component is measured.The measured temperature distribution indicates the generated magneticfield distribution and presence of hot spots. The magnitude and phasesapplied to the one or more coils can be controlled to make thetemperature distribution more uniform and reduce the hot spots asdescribed herein. In certain embodiments, the shape and position of theone or more coils can be adjusted to make the temperature distributionand the magnetic field distribution more uniform.

During the manufacturing process, a shield can be placed adjacent to themagnetic component. The location and shape of one or more openings ofthe shield can be determined based on the measured temperaturedistribution. For example, the one or more openings of the shield can bepositioned to be aligned with regions of high temperature of themagnetic component. The shape of the one or more openings can beselected to conform to the high temperature regions of the magneticcomponent. For example, the one or more openings can be shaped toconform to regions with temperatures above a threshold value. Suchthreshold value can be predetermined from separate measurements fordifferent types of magnetic elements, where the threshold value isidentified to be below the damaging temperature of the specific type ofmagnetic element. In some embodiments, the depth of the one or moreopenings can depend on the measured temperature distribution. Forexample, an opening aligned with a region of higher temperature can havea larger depth compared to another opening with a region of lowertemperature. This is because the induced magnetic fields can extendfurther for the region with higher temperature.

The above-mentioned processes can be implemented while assembling thewireless power transfer system. In certain embodiments, a calibrationmeasurements can be carried out the relation between the type, shape,arrangement of magnetic elements, the shape, positioning of coils, themagnitude and phases of applied currents, the induced temperaturedistribution and high temperature threshold values. The data obtained bythe calibration measurements can be saved in a library (e.g., electronicdatabase), which can be used as a reference during assembly of thesystem. The temperature measurements can utilize temperature sensorswhich are attached to various locations of the apparatus being measured.In some embodiments, the temperatures sensor can be a camera (e.g.,infra-red camera) to capture a thermal image.

Furthermore, the above mentioned techniques can be implemented after themanufacture of the apparatus. For example, during operation ormaintenance of the system, a user can measure the temperaturedistribution and control parameters of the system. The user can controlthe magnitude and phase of applied currents to make the temperaturedistribution more uniform. In certain embodiments, the location, shapeand depth of the openings can be reconfigured to conform to the changeof temperature distribution over time. The reconfigured can be achievedby, for example, molding, milling and/or moving parts of the shield byactuators. These processes be implemented during wireless power transferof the system. These approaches can be used to maintain the system tooperate under efficient power transfer and nonhazardous conditions andallow the system to be robust to changes in the coils, magneticcomponent and/or shield caused by vibration, thermal shocks andmechanical shocks.

These techniques can be used to take into account the fabricationimperfections of the magnetic component, coils and shield. For example,the magnetic component may have an imperfect surface after fabricationand the operation parameters of the can be set to take such imperfectioninto account to have more uniform field distribution. Moreover, thetechniques can be used to take into account any imperfections of theelements (e.g., magnetic component, coils, shield) arising due to use ofthe elements over time.

The disclosed techniques can be implemented for low operatingfrequencies where a shield can have higher loss properties than at highoperating frequencies. The operating frequency of a wireless powertransfer system can be chosen as the frequency of minimum loss of thecombined contribution of losses of an apparatus including elements suchas a shield, coil, magnetic component and electronics such as amplifiersand DC-AC converters of the system. For example, the shield can havelower losses as the operating frequency increases, and the coil can havelower losses as long as the frequency is low enough that radiativelosses in the coil are lower than ohmic losses in the coil. On the otherhand, the electronics can have higher losses as the operating frequencyincreases. An optimum frequency can exist where the combined losses canbe minimum. In addition, the operating frequency of a wireless powertransfer system may be chosen to exist within certain pre-specifiedfrequency bands determined by a regulatory agency, a standardscommittee, a government or military organization. In some cases, thecoil and shield designs are optimized to operate at a specifiedfrequency and/or within a certain frequency range. For example, such anoperating frequency can be about 85 kHz. As the shield can have higherlosses at 85 kHz than at higher frequencies, the disclosed techniquescan be used to have one or more openings in the shield to reduce lossesinduced within the shield. In some embodiments, the operating frequencycan be at about 145 kHz. In high power applications, the losses of theelectronics are typically lower for operating frequencies below 200 kHz,and thus certain high power applications are designed to operate at 20kHz, 50 kHz, 85 kHz, and 145 kHz. In low power applications (e.g., lowpower consumer electronics), certain applications are designed tooperate at the Industrial, Scientific and Medical (ISM) frequencies,where conducted and radiated emissions are not subject to regulatoryrestrictions. The ISM frequencies include 6.78 MHz, 13.56 MHz and manyharmonics of 13.56 MHz.

Techniques described in relation to FIGS. 2-24C can be applied to apower receiving apparatus. For example, a power receiving apparatus caninclude a coil, a shield and a magnetic component which has gaps betweenits magnetic elements. Hence, the power receiving apparatus canexperience similar magnetic field penetration into the shield leading toenergy loss, as described herein in relation to a power transmittingapparatus. Therefore, the techniques described above in relation to apower transmitting apparatus are equally applicable to a power receivingapparatus.

Techniques described in relation to FIGS. 2-24C can be applied to apower repeating apparatus. For example, a power repeating apparatus caninclude a coil, a shield and a magnetic component, which has gapsbetween its magnetic elements. Hence, the power repeating apparatus canexperience similar magnetic field penetration into the shield leading toenergy loss, as described herein in relation to a power transmitting andpower receiving apparatuses. The techniques described above in relationto a power transmitting apparatus and a power receiving apparatus areequally applicable to a power repeating apparatus, which wirelesslyreceives power from one apparatus and wirelessly transfer power toanother apparatus.

Quality Factors and Operating Conditions

Generally, wireless power transfer may occur between the source andreceiver resonators by way of multiple source resonators and/or multipledevice resonators and/or multiple intermediate (also referred as“repeater” or “repeating”) resonators.

The source resonators, receiver resonators, and repeater resonatorsdisclosed herein can each be an electromagnetic resonator capable ofstoring energy in fields (e.g., electric fields, magnetic fields). Anyone of the resonators can have a resonant frequency f=ω/2π, an intrinsicloss rate Γ, and a Q-factor Q=ω/(2Γ) (also referred as “intrinsic”quality factor in this disclosure), where ω is the angular resonantfrequency. A resonator can have a capacitance (C) and inductance (L)that defines its resonant frequency f according to equation 1 (Eq. (1))below:

$\begin{matrix}{f = {\frac{\omega}{2\pi} = {\frac{1}{2\pi}{\sqrt{\frac{1}{LC}}.}}}} & (1)\end{matrix}$

In some embodiments, any one of a source resonator, a receiverresonator, and/or a repeater resonator can have a Q-factor that is ahigh Q-factor where Q>100 (e.g., Q>100, Q>200, Q>300, Q>500, Q>1000).For example, a wireless power transfer system can include one or moresource resonators, and at least one of the source resonators having aQ-factor of Q₁>100 (e.g., Q₁>200, Q₁>300, Q₁>500, Q₁>1000). The wirelesspower transfer system can include one or more receiver resonators, andat least one of the receiver resonators can have a Q-factor of Q₂>100(e.g., Q₂>200, Q₂>300, Q₂>500, Q₂>1000). The wireless power transfersystem can include one or more repeater resonators, and at least one ofthe repeater resonators can have a Q-factor of Q₃>100 (e.g., Q₃>200,Q₃>300, Q₃>500, Q₃>1000).

Utilizing high Q-factor resonators can lead to large energy transferefficiency between at least some or all of the resonators in thewireless power transfer system. Resonators with high Q-factors cancouple strongly to other resonators such that the “coupling time”between resonators is shorter than the “loss time” of the resonators. Asa result, the energy transfer rate between resonators can be larger thanthe energy dissipation rate of individual resonators. Energy cantherefore be transferred efficiently between resonators at a rate higherthan the energy loss rate of the resonators, which arises from heatingand radiative losses in the resonators.

In certain embodiments, for a source-receiver resonator pair withQ-factors Q_(i) and Q_(j) (i=1, j=2), for a source-repeater resonatorpair with Q factors Q_(i) and Q_(j) (i=1, j=3), and/or for areceiver-repeater resonator pair with Q factors Q_(i) and Q_(j) (i=2,j=3), a geometric mean √{square root over (Q_(i)Q_(j))} can be largerthan 100 (e.g., √{square root over (Q_(i)Q_(j))}>200, √{square root over(Q_(i)Q_(j))}>300, √{square root over (Q_(i)Q_(j))}>500, √{square rootover (Q_(i)Q_(j))}>1000). Any one of the source, receiver, and repeaterresonators can include one or more of the coils described in thefollowing sections. High-Q resonators and methods for transferring powerusing such resonators are described, for example, in commonly owned U.S.patent application Ser. No. 12/567,716, published as US PatentApplication Publication 2010/0141042, and issued as U.S. Pat. No.8,461,719 on Jun. 11, 2013; U.S. patent application Ser. No. 12/720,866,published as US Patent Application Publication 2010/0259108, and issuedas U.S. Pat. No. 8,587,155 on Nov. 19, 2013; U.S. patent applicationSer. No. 12/770,137, published as U.S. Patent Application Publication2010/0277121; U.S. patent application Ser. No. 12/860,375, published asUS Patent Application Publication 2010/0308939; U.S. patent applicationSer. No. 12/899,281, published as US Patent Application Publication2011/0074346; U.S. patent application Ser. No. 12/986,018, published asU.S. Patent Application Publication 2011/0193416; U.S. patentapplication Ser. No. 13/021,965, published as US Patent ApplicationPublication 2011/0121920; U.S. patent application Ser. No. 13/275,127,published as US Patent Application Publication 2012/0119569; U.S. patentapplication Ser. No. 13/536,435, published as US Patent ApplicationPublication 2012/0313742; U.S. patent application Ser. No. 13/608,956,published as US Patent Application Publication 2013/0069441; U.S. patentapplication Ser. No. 13/834,366, published as US Patent ApplicationPublication 2013/0221744; U.S. patent application Ser. No. 13/283,822,published as US Patent Application Publication No. 2012/0242225, issuedas U.S. Pat. No. 8,441,154 on May 14, 2013; U.S. patent application Ser.No. 14/059,094; and U.S. patent application Ser. No. 14/031,737. Thecontents of each of the foregoing applications are incorporated hereinby reference.

In some embodiments, a resonator of any of the types disclosed herein(e.g., source, receiver, repeater resonators) can include a coil formedof a conductive material. In certain embodiments, the resonator can havea resonance with a resonant frequency defined by an inductance andcapacitance of the coil as described by Eq. (1) In this disclosure, thecoil is also referred to interchangeably as a “coil structure.”

In certain embodiments, the coil can be connected to at least onecapacitor, and the resonator can have a resonance with a resonatorfrequency defined by a combined inductance and combined capacitance ofthe coil-capacitor structure as described by Eq. (1) In this disclosure,the combination of the coil and the capacitor is also referred tointerchangeably as a “coil-capacitor structure.”

In certain embodiments, an apparatus can include a coil wound around orpositioned above and/or near-by a magnetic component (e.g., ferritematerial). The magnetic component can enhance an induced magnetic fluxdensity and can shield from nearby absorbing materials to reduce energylosses by such materials. In this disclosure, the combination of thecoil and the magnetic component is also referred to interchangeably as a“coil-magnetic component structure.” A coil-magnetic component structuremay or may not include a capacitor connected to the coil. Acoil-magnetic component structure can have a resonant frequency definedby a combined inductance and combined capacitance of the coil structureand the magnetic component, or the coil-capacitor structure and themagnetic component, and a quality factor. In this disclosure, thequality factor Q_(total) of the coil-magnetic component structure,Q_(total), can be expressed according to:

$\begin{matrix}{{\frac{1}{Q_{total}} = {\frac{R_{total}}{\omega\; L_{total}} = {{\frac{1}{Q_{coil}} + \frac{1}{Q_{\mu}}} = {\frac{R_{coil}}{\omega\; L_{total}} + \frac{R_{\mu}}{\omega\; L_{total}}}}}},} & (2)\end{matrix}$where R_(total) and L_(total) is the total effective resistance andinductance of the coil-magnetic component structure, respectively.R_(coil) and R_(μ) are the effective resistance contributed by the coiland the magnetic component, respectively. In Eq. (2), Q_(coil) can beconsidered as the quality factor of the configuration assuming alossless magnetic component, and Q_(μ) can be considered as the qualityfactor contributed by the magnetic component (e.g., ferrite material)with its loss to the coil structure or the coil-capacitor structure.

In some embodiments, a power transmitting apparatus can include acoil-magnetic component structure, and a shield positioned adjacent tothe coil-magnetic component structure. Such a power transmittingapparatus can be described to have a quality factor Q_(trans). When theshield is present, the quality factor Q_(trans) of the powertransmitting apparatus can be different from the quality factorQ_(total) of the coil-magnetic component structure (when isolated fromthe shield) due to the shield perturbing the quality factor, i.e.,because the shield alters the magnetic field distribution and thereforethe effective inductance of the coil-magnetic component structure.Taking into account the contributions from the shield, the qualityfactor Q can be expressed as:

$\begin{matrix}{{\frac{1}{Q_{trans}} = {\frac{R_{total}}{\omega\; L_{total}} = {{\frac{1}{Q_{coil}^{\prime}} + \frac{1}{Q_{\mu}^{\prime}} + \frac{1}{Q_{shield}}} = {\frac{R_{coil}}{\omega\; L_{total}} + \frac{R_{\mu}}{\omega\; L_{total}} + \frac{R_{shield}}{\omega\; L_{total}}}}}},} & (3)\end{matrix}$where R_(total) and L_(total) is the total effective resistance andinductance of the configuration including the coil-magnetic componentstructure and the shield, respectively. The parameters described in Eq.(3) can be different from that described in Eq. (2). For example,L_(total) in Eq. (3) can be different from that in Eq. (2). R_(coil),R_(μ) and R_(shield) are the effective resistances contributed by thecoil, the magnetic component and the shield, respectively. R_(coil) andR_(μ) may be the same as in Eq. (2), when assumed that they are notaffected by the presence of the shield. In Eq. (3), Q′_(coil) can beconsidered as the quality factor of the configuration assuming alossless magnetic component and a lossless shield. Q′_(μ) can beconsidered as the quality factor contributed by the magnetic componentwith its loss and assuming a lossless shield. In this disclosureQ_(shield) is referred to as a quality factor contributed by the shield.

In some embodiments, Q_(trans) can be measured or calculated. R_(total)and L_(total) can be calculated from the obtained Q_(trans). Anothermeasurement or calculation without the presence of the shield can becarried out to obtain R_(coil)+R_(μ) in Eq. (3) assuming they are notaffected by the presence of the shield. Then, R_(shield) can becalculated by subtracting R_(coil)+R_(μ) from R_(total). Further,Q_(shield) can be obtained using the calculated R_(shield) and L_(total)based on the relations described in Eq. (3).

Hardware and Software Implementation

FIG. 25 shows an example of an electronic controller 103, which may beused with the techniques described here. As mentioned earlier, theelectronic controller 103 can be used to control power transfer of awireless power transferring system, for example, by changing poweroutput of a power source, adjusting operation and/or resonantfrequencies and adjusting impedance matching networks. In someembodiments, the electronic controller 103 can be directly connected toor wirelessly communicate with various elements of the system.

Electronic controller 103 can include a processor 2502, memory 2504, astorage device 2506 and interfaces 2508 for interconnection. Theprocessor 2502 can process instructions for execution within theelectronic controller 103, including instructions stored in the memory2504 or on the storage device 2506. For example, the instructions caninstruct the processor 2502 to determine parameters of the system suchas efficiency of power transfer, operating frequency, resonantfrequencies of resonators and impedance matching conditions. In certainembodiments, the processor 2502 is configured to send out controlsignals to various elements (e.g., power source, power transmittingapparatus, power receiving apparatus, power repeating apparatus,impedance matching networks) to adjust the determined parameters. Forexample, control signals can be used to tune capacitance values ofcapacitors in an impedance matching network. In certain embodiments,control signals can be used to adjust operation frequency of a powersource. Control signals can change capacitance value of a capacitor in aresonator to tune its resonant frequency.

The memory 2504 can store information of optimized parameters of thesystem. For example, the information can include optimized impedancematching conditions for various levels of power output from the powersource. In certain embodiments, the memory 2504 can store informationsuch as resonant frequencies of resonator and magnetic properties (e.g.,magnetic permeability depending on power levels) of magnetic componentsin the system, which can be used by the processor 2502 for determiningsignals to be sent out to control various elements in the system.

The storage device 2506 can be a computer-readable medium, such as afloppy disk device, a hard disk device, an optical disk device, or atape device, a flash memory or other similar solid state memory device,or an array of devices, including devices in a storage area network orother configurations. The storage device 2506 can store instructionsthat can be executed by processor 2502 described above. In certainembodiments, the storage device 2506 can store information described inrelation to memory 2504.

In some embodiments, electronic controller 103 can include a graphicsprocessing unit to display graphical information (e.g., using a GUI ortext interface) on an external input/output device, such as display2516. The graphical information can be displayed by a display device(device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display)monitor) for displaying information. A user can use input devices (e.g.,keyboard, pointing device, touch screen, speech recognition device) toprovide input to the electronic controller 103. In some embodiments, theuser can monitor the display 2516 to analyze the power transferconditions of the system. For example, when the power transfer is not inoptimum condition, the user can adjust parameters (e.g., power transferlevel, capacitor values in impedance matching networks, operationfrequency of power source, resonant frequencies of resonators) byinputting information through the input devices. Based on the receiveinput, the electronic controller 103 can control the system as describedabove.

In some embodiments, the electronic controller 103 can be used tomonitor hazardous conditions of the system. For example, the electroniccontroller 103 can detect over-heating in the system and provide analert (e.g., visual, audible alert) to the user through its graphicaldisplay or audio device.

In certain embodiments, electronic controller 103 can be used to controlmagnitudes and phases of currents flowing in one or more coils of thewireless power transfer system. For example, processor 2502 cancalculate and determine the magnitudes and phase of currents to besupplied to coils in a power transmitting apparatus. The determinationcan be based on the monitored power transfer efficiency and informationstored in memory 2504 or storage 2506.

A feedback signal can be received and processed by the electroniccontroller 103. For example, the electronic controller 103 can include awireless communication device (e.g., radio-frequency, Bluetoothreceiver) to receive information from either or both of a powertransmitting apparatus and a power receiving apparatus (which can haveits own wireless communication device). In some embodiments, thereceived information can be processed by processor 2502, which canfurther send out control signals to adjust parameters of the system asdescribed above. For example, the control signals can be used to adjustthe magnitudes and phases of currents flowing in one or more coils ofresonators in the system to increase the power transfer efficiency.

Various embodiments of the systems and techniques described here can berealized by one or more computer programs that are executable and/orinterpretable on the electronic controller 103. These computer programs(also known as programs, software, software applications or code)include machine instructions for a programmable processor, and can beimplemented in a high-level procedural and/or object-orientedprogramming language, and/or in assembly/machine language. For example,computer programs can contain the instructions that can be stored inmemory 2504 and storage 2506 and executed by processor 2502 as describedabove. As used herein, the terms “computer-readable medium” refers toany computer program product, apparatus and/or device (e.g., magneticdiscs, optical disks, memory, Programmable Logic Devices (PLDs)) used toprovide machine instructions and/or data to a programmable processor,including a machine-readable medium that receives machine instructions.

Generally, electronic controller 103 can be implemented in a computingsystem to implement the operations described above. For example, thecomputing system can include a back end component (e.g., as a dataserver), or a middleware component (e.g., an application server), or afront end component (e.g., a client computer having a graphicaluser-interface), or any combination therefor, to allow a user toutilized the operations of the electronic controller 103.

The electronic controller 103 or one or more of its elements can beintegrated in a vehicle. The electronic controller 103 can be utilizedto control and/or monitor wireless power charging of a battery installedin the vehicle. In some embodiments, the display 2516 can be installedadjacent to the driving wheel of the vehicle so that a user may monitorconditions of the power charging and/or control parameters of the powercharging as described in relation to FIG. 25. The display 2516 can alsovisualize information traffic information and road maps based on GlobalPositioning System (GPS) information. Any of the elements such as theprocessor 2502, memory 2504 and storage device 2506 can be installed inthe space behind the display 2516, which can visualize the data processby those elements.

While this disclosure contains many specific implementation details,these should not be construed as limitations on the scope of thedisclosure, but rather as descriptions of features specific toparticular embodiments. Features that are described in this disclosurein the context of separate embodiments can also generally be implementedin combination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can generally be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

In addition to the embodiments disclosed herein, other embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. An apparatus for wireless power transfer, theapparatus comprising: a plurality of adjacent magnetic elementspositioned in a plane and defining a gap; a coil comprising one or moreloops of conductive material positioned, at least in part, on a firstside of the plane and on both sides of the gap; and a conductive shieldpositioned on a second side of the plane and comprising an openingaligned with the gap.
 2. The apparatus of claim 1, wherein theconductive shield is oriented substantially parallel to the plane. 3.The apparatus of claim 1, wherein the gap is not filled with a solidmaterial.
 4. The apparatus of claim 1, further comprising a dielectricmaterial positioned in the gap to at least partially fill the gap. 5.The apparatus of claim 1, further comprising a magnetic material havinga magnetic permeability different from a magnetic permeability of themagnetic elements and positioned in the gap to at least partially fillthe gap.
 6. The apparatus of claim 1, wherein the loops are positionedentirely on the first side of the plane.
 7. The apparatus of claim 1,wherein: during operation, the coil generates a magnetic field thatoscillates in a first direction parallel to the plane; the gapcorresponds to a spacing between magnetic elements in a directionparallel to the first direction; and the opening comprises a width thatextends in a direction parallel to the first direction.
 8. An apparatusfor wireless power transfer, the apparatus comprising: a plurality ofadjacent magnetic elements positioned in a plane and defining a gap; acoil comprising one or more loops of conductive material positioned, atleast in part, on a first side of the plane; and a conductive shieldpositioned on a second side of the plane and comprising a depressionformed in a surface of the shield facing the plane, and aligned with thegap.
 9. The apparatus of claim 8, wherein the depression is positionedto reduce interactions between magnetic flux crossing the gap and theconductive shield.
 10. The apparatus of claim 8, wherein the coil ispositioned entirely on the first side of the plane.
 11. The apparatus ofclaim 8, wherein the one or more loops of conductive material encirclean axis oriented in a direction perpendicular to the plane.
 12. Theapparatus of claim 8, wherein the depression has a cross-sectionalprofile that corresponds to at least one of a triangular shape, atrapezoidal shape, and a shape comprising curved edges.
 13. Theapparatus of claim 8, wherein at least a portion of the conductiveshield is oriented parallel to the plane.
 14. The apparatus of claim 8,further comprising a dielectric material positioned in the gap.
 15. Theapparatus of claim 8, further comprising a filler material positioned inthe gap, wherein a magnetic permeability of the filler material isdifferent from a magnetic permeability of the plurality of magneticelements.
 16. The apparatus of claim 8, wherein the depression compriseslateral surfaces that are angled relative to the plane.
 17. Theapparatus of claim 8, wherein: during operation of the apparatus, thecoil generates a magnetic field oscillates in a first direction withinthe plurality of magnetic elements; the gap corresponds to a spacingbetween magnetic elements in a direction parallel to the firstdirection; and the depression comprises a width that extends in adirection parallel to the first direction.
 18. An apparatus for wirelesspower transfer, comprising: a plurality of adjacent planar magneticelements positioned in a plane and defining a gap in the plane; a coilcomprising one or more loops of conductive material; and a conductiveshield positioned on a second side of the plane and comprising at leastone of a depression and an opening formed in a surface of the shield,wherein the at least one of the depression and the opening is alignedwith the gap, wherein the coil is oriented so that during operation ofthe apparatus, the coil generates an average magnetic field oriented ina first direction parallel to the plane.
 19. The apparatus of claim 18,wherein the coil comprises a first plurality of loops and a secondplurality of loops connected to the first plurality of loops, andwherein the first and second pluralities of loops are arranged so thatduring operation of the apparatus, electrical current circulates in afirst rotational direction in the first plurality of loops and in asecond rotational direction opposite to the first rotational directionin the second plurality of loops.
 20. The apparatus of claim 18, whereina width of the gap extends in a second direction, and wherein an anglebetween the first and second directions is 10° or less.